Illumination apparatus and a liquid crystal projector using the illumination apparatus

ABSTRACT

An illumination apparatus includes a reflector including a parabolic or ellipsoidal mirror, a light source arranged near a (first) focal point of the reflector, and a front mirror having a transparent window and a mirror surface symmetrical about the light axis. Luminous flux emitted from the light source is reflected from the reflector. In the case of the parabolic mirror, the front mirror has the same size as an entrance of an output light utilizing optical system, and the luminous flux exits toward the optical system as collimated light. In the case of the ellipsoidal mirror, the front mirror is arranged between two focal points of the ellipsoidal mirror, and the luminous flux is directed toward the second focal point. However, at least one part of the luminous flux is reflected from the front mirror and returned toward the first focal point.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an illumination apparatussuitable for illuminating a rectangular object such as a liquid crystalpanel, and a liquid crystal projector using such an illuminationapparatus.

[0003] 2. Description of the Related Art

[0004] As for an illumination optical system for uniformly illuminatinga rectangular object such as a liquid crystal panel, an integratoroptical system in which two fly-eye lens-arrays are combined is knownfrom, for example, Japanese Laid-Open Patent Application No. 3-111806.

[0005] The integrator optical system shown in the above patentapplication divides a luminous flux originating from a light source witha reflector such as a parabolic reflector, an ellipsoidal reflector anda hyperbolic reflector, by multiple rectangular focusing lensesconstituting a first fly-eye lens-array to form secondary light sourceimages. A convolution of the secondary light source images is imaged onone illuminated object through a second fly-eye lens-array havingmultiple focusing lenses corresponding to the multiple rectangularfocusing lenses of the first fly-eye lens-array. According to such anintegrator optical system, it is believed that intensity distribution oflight on a surface of the illuminated object can be made almost uniformas well as usability of light from the light source being improved.Particularly, the usability of light and uniformity of intensitydistribution can be improved by matching shapes of respective focusinglenses of the first and the second fly-eye lens-array to an aspect ratioof the rectangular illuminated object, for example, by making thefocusing lens into a rectangular shape having the ratio of a long sideand a short side of 4:3.

[0006] That is, in Japanese Laid-Open Patent Application No. 3-111806,an integrator optical system using a first macro-lens array, of whichthe common name is fly-eye lens plate, having rectangular lenses on afirst lens plate and a second macro-lens array having lensescorresponding to the lenses on the first lens plate can makeillumination matching an aspect ratio of an illuminated object. Then, asfor an example of a configuration at the light source side in order tomake the size of the integrator optical system compact, a light sourceis placed at a first focal point of an ellipsoidal mirror, a collimatorlens is located behind a second focal point of the mirror, and anintegrator optical system is arranged behind the collimator lens, asshown in FIG. 1 that is also drawn in-Japanese Laid-Open PatentApplication No. 3-111806.

[0007] Also, FIG. 2 shows a configuration example including a parabolicmirror instead of the ellipsoidal mirror shown in FIG. 1.

[0008] In FIG. 1 and FIG. 2, basically, illumination with an aspectratio suitable for a liquid crystal panel 103 as an illuminated objectis performed using a first macro-lens array or a first fly-eyelens-array 101 having rectangular lenses on a first lens plate in anintegrator optical system 100 and a second macro-lens array or a secondfly-eye lens-array 102 having lenses respectively corresponding to therectangular lenses of the first fly-eye lens-array.

[0009] Then, at the light source side of the configuration shown in FIG.1, light generated from a light source 105 arranged at a first focalpoint F1 of an ellipsoidal mirror 104 as a reflector, is reflected fromthe ellipsoidal mirror 104, and is focused to a second focal point F2,and enters the integrator optical system 100 by a collimator lens 107.

[0010] Also, at the light source side of the configuration shown in FIG.2, light generated from a light source 105 arranged at a focal point F1of a parabolic mirror 104 as a reflector is reflected from the surfaceof the parabolic mirror 104, collimated, focused to a pointcorresponding to a second focal point F2 of an ellipsoid having a firstfocal point at F1 by a convex lens 106, then enters the integratoroptical system 100 by a collimator lens 107.

[0011] Herein, in FIG. 1 and FIG. 2, a polarization alignment prismarray for aligning polarization of light generated from the light sourcewith a mixture of a p-polarization component and a s-polarizationcomponent to only the s-polarization component or the p-polarizationcomponent is indicated with the numeral 108. Two lenses are alsoindicated with the numerals 109 and 110 in the FIG. 1 and FIG. 2.

[0012] According to the configuration example shown in FIG. 2, althoughthe number of the members is one more than that of the example shown inFIG. 1, the size of a reflector and the position of a focal point of thereflector, which represents a parabolic mirror and an ellipsoid mirror,etc., can be freely defined.

[0013] Also, according to Japanese Laid-Open Patent Application No.10-161065, an illumination apparatus is proposed, in which a collimatedlight obtained from a light source placed at a focal point of aparabolic mirror is focused by a convex lens, collimated again by aconcave lens and led to a polarization conversion means or an integratoroptical system in order to decrease the size of the integrator opticalsystem.

[0014]FIG. 3 shows an illumination apparatus based on the idea ofJapanese Laid-Open Patent Application No. 10-161065. As compared withthe illumination apparatus shown in FIG. 2, a collimating lens 111 isarranged at the near side or light source side of a point correspondingto a second focal point F2 of an ellipsoid having a first focal point atF1, wherein the collimator lens 107 is omitted.

[0015] Furthermore, according to Japanese Laid-Open Patent ApplicationNo. 5-264904, as shown in FIG. 4, similar to the case of the abovementioned Japanese Laid-Open Patent Application No. 3-111806, it isproposed that light generated from a light source 105 placed at a firstfocal point F1 of an ellipsoidal mirror 104 or a parabolic mirror is ledto an integrator optical system 100 through a collimator lens 107arranged behind a second focal point F2. Luminous flux not reflected bythe surface of the ellipsoidal mirror 104 returns to the light source105 using a concave mirror-112 having a spherical center at the firstfocal point F1. Thus most of the luminous flux generated from the lightsource 105 can be utilized.

[0016] Also, according to Japanese Laid-Open Patent Application No.2001-66697, as shown in FIG. 5, it is proposed that a reflection film214 on a part of a vessel 213 of a lamp 212 attached to a reflector 211is formed to be a light source having a substantially spherical mirrorstructure so that the luminous flux generated from the light source isreturned toward the reflector 211 side to be effectively utilized.

[0017] The idea shown in the aforementioned Japanese Laid-Open PatentApplication No. 3-111806 or in FIG. 1 and FIG. 2 is that luminous fluxoriginating from the light source 105 is focused at once and collimatedby the collimator lens 107 to decrease the whole size of the integratoroptical system 100, thus achieving the comprehensive object. However,according to the configuration, the size of an image of the light sourceat the focal point, at which luminous flux originating from the lightsource 105 is focused again, is magnified to several times of the sizeof the original image of the light source and collimation by acollimator lens 107 is limited so that usability of light in theintegrator optical system 100 is lowered. The property in the case ofuse of an ellipsoidal mirror instead of the parabolic mirror 104 showsthe same tendency as the case of the combination of the parabolic mirror104 and the convex lens 107.

[0018] Furthermore, in the case of the configuration example shown inFIG. 1, as a coverage angle θ of the ellipsoidal mirror 104 isincreased, a maximum incidence angle ψ is also increased, so thatefficiency at the collimator lens is reduced and the illuminationapparatus becomes complex because of needing many lenses, etc.

[0019] Also in the case of the configuration as shown in JapaneseLaid-Open Patent Application No. 10-161065 or in FIG. 3, in principle,collimated light exiting from the collimating lens 111 that is a concavelens has the same degree of collimation as collimated light obtained byuse of the collimator lens 107 shown in FIG. 2. As similar to theaforementioned example in the prior art, even if an ellipsoidal mirroris employed and the collimating lens 111 is placed at the near side ofthe second focal point F2, the property shows a same tendency as thecase of the combination of the parabolic mirror 104 and the collimatinglens 111.

[0020] Moreover, in the case of Japanese Laid-Open Patent ApplicationNo. 5-264904 like the example shown in FIG. 4, the concave mirror 112having a spherical center at the first focal point F1 is arranged andlight not covered by the surface of the parabolic mirror 104 isreflected and utilized to improve the usability of the luminous fluxgenerated from the light source 105. However, the idea that luminousflux is focused at once and collimated by the collimator lens 107 todecrease the whole size of the integrator optical system 100, thusachievement of the comprehensive object is the same idea as the examplein the prior art shown in FIG. 1. Hence, similar to the configurationshown in FIG. 1, the size of an image of the light source at the focalpoint, at which luminous flux emitted from the light source 105 isfocused again, is magnified to several times of the size of an originalimage of the light source and collimation by a collimator lens islimited so that light usability of the integrator optical system 100 islowered.

[0021] Furthermore, the configuration example shown in FIG. 4 is similarto the case of Japanese Laid-Open Patent Application NO. 3-111806 inthat as a coverage angle θ of the ellipsoidal mirror 104 is increased, amaximum incidence angle ψ is also increased, so that efficiency at thecollimator lens is reduced and an illumination apparatus becomes complexbecause of needing many lenses, etc.

[0022] Also, in the case of Japanese Laid-Open Patent Application No.2001-66697 like the example shown in FIG. 5, light reflected from aspherical mirror magnifies an arc image of the light source as if therewere a group of arc images at the position away from the same degree ofa distance from the vessel center to the mirror as indicated by dashedlines in FIG. 5. In other word, since the arc image is present at aposition away from the focal point of the reflector, it isdisadvantageous that parallelism of luminous flux from the reflector 211obtained via the spherical reflection mirror is extremely lowered ascompared to light directly coming from the arc. Moreover, at a pipe wallreaching to near 1000° C., reflection property is lowered for a shorttime period. Even if the lamp is slightly floated from the pipe wall asshown in FIG. 6, degradation time of the lamp may become slightlylonger, but the lamp must be frequently exchanged in practice.

SUMMARY OF THE INVENTION

[0023] Accordingly, it is a general object of the present invention toprovide an illumination apparatus reducing the size of an output lightutilizing optical system such as an integrator optical system andimproving the usability of luminous flux originating from a lightsource, and a liquid crystal projector using such an illuminationapparatus.

[0024] A more specific object of the present invention is to provide anillumination apparatus improving parallelism of luminous flux enteringan output light utilizing optical system such as an integrator opticalsystem, for example, capable of reducing the size of an image of a lightsource on a surface of a second fly-eye lens-array of the integratoroptical system to point source-like, and a liquid crystal projectorusing such an illumination apparatus.

[0025] A more specific object of the present invention is to provide anillumination apparatus capable of taking a substantially large coverageangle, making an incidence angle to a collimation means small, andobtaining a collimated light efficiently.

[0026] A more specific object of the present invention is to provide anillumination apparatus capable of emitting high-quality homogeneousilluminating radiation onto an illuminated surface.

[0027] To achieve one of the above objects, the present inventionprovides an illumination apparatus in which at least one part of areflector is a first parabolic mirror, a light source is arranged near afocal point of the first parabolic mirror, and collimated light that isemitted from the light source and reflected from the first parabolicmirror exits toward an output light utilizing optical system, wherein afront mirror with a window having no mirror surface and a-transparency,whose size is substantially the same-as the size of an entrance part ofthe output light utilizing optical system, and with a mirror surface atthe light source side that is symmetrical about a light axis of thecollimated light extending through the position of the focal point ofthe first parabolic mirror, is arranged on the light path of thecollimated light.

[0028] Accordingly, while the collimated light reflected from the firstparabolic mirror basically exits through the window having no mirrorsurface of the front mirror toward the output light utilizing opticalsystem, light generated from the light source and not directly impingingon the first parabolic mirror can be reflected from the mirror surfaceat the light source side that is symmetrical about the light axis of thecollimated light extending through the position of the focal point ofthe first parabolic mirror, returned back to the first parabolic mirror,reflected again by the first parabolic mirror, and exiting as collimatedlight through the position of the focal point. Hence, the parallelism ofthe luminous flux exiting toward the output light utilizing opticalsystem is not decreased and most of the luminous flux of the lightgenerated from the light source can be utilized efficiently.Furthermore, since the size of the window having no mirror surface and atransparency, being substantially the same as the size of an entrancepart of the output light utilizing optical system, can be controlled,the size of the output light utilizing optical system can be controlledto be small.

[0029] The present invention provides the illumination apparatus asdescribed above, wherein the front mirror is provided to a front glassattached to an exit of the first parabolic mirror as one unit.

[0030] According to the present invention as described above, theconfiguration of the illumination apparatus can be made simple and theprecision with respect to the orthogonality of the front mirror to thelight axis, etc., can be maintained, since the front mirror is providedto the front glass attached to the exit of the first parabolic mirror asone unit.

[0031] The present invention provides the illumination apparatusdescribed above, wherein the front mirror is arranged between the frontglass attached to an exit of the first parabolic mirror and the lightsource.

[0032] Accordingly, in realization of the invention described above, thewhole size of the illumination apparatus can be made more compact. Also,light generated from a light source can be reflected and returned by thefront mirror before the light diverges, to control the divergence angleof the light to become smaller.

[0033] The present invention provides the illumination apparatusdescribed above, wherein the output light utilizing optical systemcomprises an integrator optical system therein and the front mirror isprovided in combination with a first fly-eye lens-array or a membercorresponding to the first fly-eye lens-array of the integrator opticalsystem as one unit.

[0034] Accordingly, the configuration of the illumination apparatus canbe made simple and the precision with respect to the orthogonality ofthe front mirror to the light axis, etc. can be maintained, since thefront mirror is provided in combination with a first fly-eye lens arrayor a member corresponding to the first fly-eye lens-array of theintegrator optical system as one unit.

[0035] The present invention provides the illumination apparatusesdescribed above, wherein the front mirror is a plane mirror.

[0036] Accordingly, such configuration where the plane mirror isprovided so as to be orthogonal to the light axis of the collimatedlight is included in the illumination apparatuses described above.Hence, in the realization of the illumination apparatuses, it is easy tofabricate the front mirror since the front mirror is a plane mirror.

[0037] Moreover, the present invention provides an illuminationapparatus in which at least one part of a reflector is a first parabolicmirror, a light source is arranged near a focal point of the firstparabolic mirror, and collimated light emitted from the light source andreflected from the first parabolic mirror exits toward an output lightutilizing optical system, wherein the reflector comprises the firstparabolic mirror at least in a region in which the collimated lightreflected from the first parabolic mirror covers an entrance of theoutput light utilizing optical system and an ellipsoidal mirror outsidethe first parabolic mirror having a focal point common to the focalpoint of the first parabolic mirror, and a plane mirror with a windowhaving no mirror surface and a transparency, whose size is substantiallythe same size of an entrance part of the output light utilizing opticalsystem, is arranged near a minor axis of the ellipsoidal mirrorperpendicularly to the light axis of the collimated light.

[0038] Accordingly, similar to the present invention as described abovein which the plane mirror is employed as the front mirror, inparticular, since the first parabolic mirror and the ellipsoidal mirrorare combined as the reflector, attenuation of luminous flux can besuppressed by decreasing the number of reflections repeated between thereflector and the plane mirror to improve usability of the light. Inaddition, as compared to the case of utilizing only one parabolicmirror, the size of the reflector is made smaller if the parabolicmirrors have the same focal length. As a result, down-sizing of thewhole illumination apparatus can be realized without reducing theusability of the light.

[0039] The present invention provides the illumination apparatusdescribed above, wherein-the reflector comprises a second parabolicmirror existing from an end of the ellipsoidal mirror and extending tothe plane mirror near the minor axis and having a focal point common tothe focal point of the first parabolic mirror.

[0040] Accordingly, in realization of the invention described above, itis easy to make a mold for the reflector so that the surface precisionof the reflector can be improved.

[0041] The present invention provides the illumination apparatusesdescribed above, wherein the front mirror is a third parabolic mirrorhaving a focal point common to the focal point of the first parabolicmirror.

[0042] Accordingly, in realization of the illumination apparatusesaccording to the present invention as described above, parallelism ofcollimated light can be improved to create high-quality illuminationsince the front mirror is a third parabolic mirror facing the firstparabolic mirror as the reflector.

[0043] The present invention provides the illumination apparatusdescribed above, wherein the position of a point at which a straightline through the focal point and a part of the third parabolic mirror atwhich the distance from the center of the window is minimum intersectsthe first parabolic mirror is outside an intersection line of a holethrough which the light source is inserted.

[0044] Accordingly, even if the hole for inserting and mounting thelight source is taken into consideration, most of the luminous fluxemitted from the light source can be utilized to provide a moreefficient illumination apparatus.

[0045] The present invention provides the illumination apparatusesdescribed above, wherein the output light utilizing optical system has apolarization converter for aligning polarization direction on theentrance thereof and the size of the window having no mirror surface ofthe front mirror is substantially the same as the size of thepolarization converter.

[0046] Accordingly, in such a configuration where a polarizationconverter is employed to improve usability of the light, an operationand a working effect similar to those of the present inventions asdescribed above can be obtained. Particularly, by devising a structureof a polarization converter, the size of the window on the front mirrorcan also be decreased by half.

[0047] The present invention provides the illumination apparatusesdescribed above, wherein the output light utilizing optical system hasan integrator optical system on the entrance thereof and the size of thewindow having no mirror surface of the front mirror is substantially thesame as the effective size of the first fly-eye lens-array on theentrance of the integrator optical system.

[0048] The present invention provides the illumination apparatusesdescribed above, wherein the output light utilizing optical system hasan integrator optical system on the entrance thereof and the size of thewindow having no mirror surface of the front mirror is substantially thesame as an effective size of a orthogonal cylindrical lens-array on theentrance of the integrator optical system.

[0049] Accordingly, since the density of the luminous flux emitted fromthe light source is not uniform, in such configuration as an integratoroptical system, in which the luminous flux is divided into multiplesegments and the respective divided luminous flux segments areintegrated on an illuminated object again, is provided, an operation anda working effect similar to those of the present inventions as describedabove can be obtained.

[0050] The present invention provides the illumination apparatusesdescribed above, wherein the window of the front mirror has such size asa minimum distance from the light axis to a part at which the collimatedlight through the focal point of the first parabolic mirror impinges thefront mirror is larger than two times of the focal length of the firstparabolic mirror.

[0051] Accordingly, light reflected from the front mirror is effectivelyled to an exit aperture of the reflector to improve usability of theluminous flux emitted from the light source.

[0052] The present invention provides the illumination apparatusdescribed above, wherein the front mirror is held at a set position by aspring material.

[0053] Accordingly, the front mirror is not fixed by means of adhesive,etc. and the shape of the third parabolic mirror used as the frontmirror can be kept constant even in an illumination apparatus with largetemperature change, so that a highly efficient illumination apparatuscan usually be provided.

[0054] The present invention provides an illumination apparatus using anellipsoidal mirror in at least one part of a reflector, arranging alight source near a first focal point of the ellipsoidal mirror andreflecting luminous flux emitted from the light source by theellipsoidal mirror to direct the luminous flux to near a second focalpoint of the ellipsoidal mirror, wherein a front mirror, on which awindow having no mirror surface is formed at a part near the light axisextending through the first focal point and the second focal point, isarranged between the first focal point and the second focal point, andat least one part of the light reflected from the ellipsoidal mirror ofthe luminous flux emitted from the light source is reflected from thefront mirror in front of the second focal point to be returned to theellipsoidal mirror or a vicinity of the first focal point.

[0055] Accordingly, while the luminous flux reflected from theellipsoidal mirror constituting the reflector is basically directed tothe second focal point through the window of the front mirror, luminousflux generated from the light source and reflected from the front mirrorand a luminous flux generated from the light source, reflected from theellipsoidal mirror and further reflected from the front mirror can bedirected through the first focal point, reflected from the ellipsoidalmirror, passes through the window of the front mirror and directedtoward the second focal point side. Hence, a substantially largecoverage angle can be taken only by deciding the size of the window ofthe front mirror so as to utilize almost all of the luminous fluxgenerated from the light source efficiently.

[0056] The present invention provides the illumination apparatusdescribed above, wherein the front mirror is a plane mirror arrangedorthogonal to the light axis and at the position of the minor axis ofthe ellipsoidal mirror.

[0057] Accordingly, since it is basically easy to make the front mirror,which is a plane mirror, the configuration of the illumination apparatuscan be made simply. Hence, the front mirror and a front glass coveringan exit of the reflector can be provided as one unit, etc., andprecision with respect to the orthogonality of the front mirror to thelight axis, etc. can be improved.

[0058] The present invention provides the illumination apparatusdescribed above, wherein the front mirror has the window at least in therange cut out by a conical surface extending from an edge of a lightsource holding hole formed on the reflector through the first focalpoint.

[0059] Accordingly, even if the light source holding hole for mountingthe light source is taken into consideration, the coverage angle istaken as large as possible in such range as the luminous flux is notunder the influence of an adverse effect by the light source holdinghole formed on the reflector, so that almost all of the luminous fluxemitted from the light source can be utilized to provide an illuminationapparatus with high efficiency.

[0060] The present invention provides the illumination apparatusdescribed above, wherein the front mirror is a spherical mirror of whosecenter is the second focal point.

[0061] Accordingly, luminous flux generated from the light source,reflected from the ellipsoidal mirror and directed to the sphericalmirror can take such a light path that the luminous flux is reflectedtoward the ellipsoidal mirror again, passes through the first focalpoint at which the light source is placed, and is reflected from theellipsoidal mirror again so that the luminous flux can be efficientlydirected toward the second focal point side.

[0062] The present invention provides the illumination apparatusdescribed above, wherein the front mirror has a window at least in therange cut out by a conical surface extending from the intersection lineof a surface orthogonal to the light axis at the first focal point andthe ellipsoidal mirror, to the second focal point.

[0063] Accordingly, the coverage angle is taken as large as possiblewithout loss of the usability of the light generated from the lightsource.

[0064] The present invention provides the illumination apparatusesdescribed above, wherein a first optical member of a collimation meansfor making collimated light is arranged behind the second focal point onthe light axis.

[0065] Accordingly, an incidence angle into the collimation means suchas a collimator lens can be made small to obtain efficiently collimatedlight.

[0066] The present invention provides the illumination apparatusesdescribed above, wherein a first optical member of a collimation meansfor making collimated light is arranged between the front mirror and thesecond focal point.

[0067] Accordingly, luminous flux directed to the second focal point canbe collimated by the collimation means such as a collimator lens so thata rear output light utilizing optical system can be closely arranged.

[0068] The present invention provides the illumination apparatusesdescribed above, wherein the window has a shape similar to the shape ofan entrance of an optical element on the entrance part of the outputlight utilizing optical system.

[0069] Accordingly, since the window of the front mirror is formed intoa shape similar to an entrance of an optical element on the entrancepart of the output light utilizing optical system, the size of theoutput light utilizing optical system can be made small by controllingthe size of the window.

[0070] The present invention provides the illumination apparatusdescribed above, wherein the optical element on the entrance part of theoutput light utilizing optical system is an integrator.

[0071] Accordingly, since density of the luminous flux emitted from thelight source is basically uneven, in such configuration where theintegrator optical system is provided to divide the luminous flux intomultiple segments and to again integrate respective divided luminousflux segments on an illuminated object again, an operation and a workingeffect similar to those of the invention described above can beobtained. That is, parallelism of the luminous flux entering theintegrator optical system can be improved and the size of the lightsource image formed on a surface of the second fly-eye lens-array in theintegrator optical system can be made small, and thus high-qualityhomogeneous illuminating radiation can be emitted for illuminating aliquid crystal panel, etc. in a liquid crystal projector.

[0072] The present invention provides the illumination apparatusdescribed above, wherein the optical element on the entrance part of theoutput light utilizing optical system is a polarization converter.

[0073] Accordingly, in such configuration where the output lightutilizing optical system includes the polarization converter to improveusability of light, an operation and a working effect similar to thoseof the invention described above can be obtained.

[0074] The present invention provides a liquid crystal projectorcomprising at least one liquid crystal panel on which an image projectedby an image information controlling unit is formed, the illuminationapparatuses described above for illuminating the liquid crystal panel asan illuminated object by the output light utilizing optical system, anda projection lens system for projecting the image formed on the liquidcrystal to a screen.

[0075] Accordingly, since the liquid crystal panel can be illuminated byluminous flux with high usability of light on the whole using theillumination apparatus described above to project the image to thescreen by the projection lens system having a relatively small aperture,the whole liquid crystal projector can be made compact.

[0076] Herein, the liquid crystal panel may be a reflection liquidcrystal panel and a transmission liquid crystal panel Particularly, inthe case of the reflection liquid crystal panel, it is most preferablethat the incidence angle of the illuminating radiation to the liquidcrystal panel should be only vertical. Also, it is practically necessarythat the incidence angle should be controlled to be in the range of afew degrees taking a tolerance for decrease of contrast intoconsideration. That is, efficient illumination can be made for theincidence angle within a few degrees of collimated light with highparallelism like the above. Also, in the case of a color display, threeliquid crystal panels corresponding to three primary colors, R, G, and Bor red, green, and blue, respectively, are commonly used in combinationwith a dispersion element, etc., for example, a dichroic prism ormirror.

BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Other objects, features and advantages of the present inventionwill become more apparent from the following detailed description whenread in conjunction with the accompanying drawings, in which:

[0078]FIG. 1 is a schematic diagram showing an optical configuration ofa first illumination apparatus in the prior art.

[0079]FIG. 2 is a schematic diagram showing an optical configuration ofa second illumination apparatus in the prior art.

[0080]FIG. 3 is a schematic diagram showing an optical configurationnear a reflector of a third illumination apparatus in the prior art.

[0081]FIG. 4 is a schematic diagram showing an optical configurationnear a reflector of a forth illumination apparatus in the prior art.

[0082]FIG. 5 is a schematic diagram showing an optical configurationnear a reflector of a fifth illumination apparatus in the prior art.

[0083]FIG. 6 is a schematic diagram showing an optical configuration ofa variation of the reflector shown in FIG. 5.

[0084]FIG. 7 is a schematic diagram showing an optical configuration ofan illumination apparatus according to the first embodiment of thepresent invention.

[0085]FIG. 8 is a schematic diagram showing an optical configuration ofan illumination apparatus according to the second embodiment of thepresent invention.

[0086]FIG. 9 is a cross-sectional diagram of a configuration near areflector showing a main part of an illumination apparatus according tothe third embodiment of the present invention.

[0087]FIG. 10 is an elevation view of the reflector shown in FIG. 9.

[0088]FIG. 11 is a cross-sectional diagram of a configuration near areflector showing a main part of an illumination apparatus according tothe fourth embodiment of the present invention.

[0089]FIG. 12 is an elevation view of the reflector shown in FIG. 11.

[0090]FIG. 13 is a schematic diagram illustrating a principle of areflector according to the fifth embodiment of the present invention.

[0091]FIG. 14 is a schematic diagram showing an optical configuration ofa practical example to which an illumination apparatus according to thepresent invention is applied.

[0092]FIG. 15 is a schematic diagram showing a main part of anillumination apparatus according to the sixth embodiment of the presentinvention, wherein (a) is a cross-sectional diagram showing aconfiguration near a reflector.

[0093]FIG. 16 is a top plan view of a polarization converter.

[0094]FIG. 17 is a schematic diagram showing an optical configuration ofan entire illumination apparatus.

[0095]FIG. 18 is a schematic diagram showing an optical configuration ofa variation of an illumination apparatus according to the presentinvention.

[0096]FIG. 19 is a schematic diagram illustrating a principle of areflector according to the seventh embodiment of the present invention.

[0097]FIG. 20 is a schematic diagram illustrating a principle of areflector according to the eighth embodiment of the present invention.

[0098]FIG. 21 is an elevation view of a window of a second parabolicmirror.

[0099]FIG. 22 is a cross-sectional diagram of a configuration near areflector showing a main part of an illumination apparatus.

[0100]FIG. 23 is an elevation view of the reflector shown in FIG. 22.

[0101]FIG. 24 is a cross-sectional diagram of a configuration near areflector showing a main part of an illumination apparatus according tothe ninth embodiment of the present invention.

[0102]FIG. 25 is an elevation view of the reflector shown in FIG. 24.

[0103]FIG. 26 is a cross-sectional diagram of a configuration near areflector showing a main part of an illumination apparatus according tothe tenth embodiment of the present invention.

[0104]FIG. 27 is an elevation view of the reflector shown in FIG. 26.

[0105]FIG. 28 is a schematic diagram showing an optical configuration ofan illumination apparatus according to the eleventh embodiment of thepresent invention.

[0106]FIG. 29 is a schematic diagram showing an optical configuration ofa liquid crystal projector according to the twelfth embodiment of thepresent invention.

[0107]FIG. 30 is a schematic diagram showing an optical configuration ofa liquid crystal projector according to the thirteenth embodiment of thepresent invention.

[0108]FIG. 31 is a schematic diagram illustrating a principle of areflector configuration of the fourteenth embodiment of the presentinvention.

[0109]FIG. 32 is a schematic diagram illustrating a principle of a morespecific reflector configuration in which a collimator lens is combined.

[0110]FIG. 33 is a schematic diagram illustrating a principle of a morespecific reflector configuration in which a collimator lens of thefifteenth embodiment of the present invention is combined.

[0111]FIG. 34 is a schematic diagram illustrating a principle of areflector configuration of the sixteenth embodiment of the presentinvention.

[0112]FIG. 35 is a schematic diagram illustrating a principle of a morespecific reflector configuration in which a collimator lens is combined.

[0113]FIG. 36 is a schematic diagram illustrating a principle of a morespecific reflector configuration in which a collimator lens of theseventeenth embodiment of the present invention is combined.

[0114]FIG. 37 is a schematic diagram of an optical configuration showinga main part of an illumination apparatus of the eighteenth embodiment ofthe present invention.

[0115]FIG. 38 is a schematic diagram of an optical configuration showinga variation of the main part of the illumination apparatus shown in FIG.37

[0116]FIG. 39 is a schematic diagram of an optical configuration showinga main part of an illumination apparatus of the nineteenth embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0117] Firstly, the first embodiment of the present invention will beillustrated with reference to FIG. 7.

[0118] In an illumination apparatus A1 of the present embodiment, arectangular liquid crystal panel 1 with an aspect ratio of alongitudinal side and a lateral side of 4:3 is an illuminated object anda condenser lens 2 laid on the front surface of the crystal paneltransmits luminous flux with minimum diameter to a projection lens afterrespective liquid crystal elements receive illuminating radiation andform an image. For such liquid crystal panel 1, the illuminationapparatus A1 of the present embodiment includes a light source 3 like apoint source, a parabolic mirror 4 as a reflector in which the lightsource 3 is arranged inside, an integrator optical system 5 as an outputlight utilizing optical system, and a focusing lens 6.

[0119] As for the light source 3, a high-pressure mercury-vapor lamp, ametal halide lamp, and a xenon lamp,.etc. have been used. The lightsource 3 is arranged at a focal point F of the parabolic mirror 4 withan inside mirror surface 4 a in the shape of a revolved parabola. Hence,the mirror surface 4 a of the parabolic mirror 4 has an optical propertyof emission of collimated light when the mirror surface 4 a receiveslight originating from the light source 3. The exit of the parabolicmirror 4 is covered with a front glass 8.

[0120] An integrator optical system 5 is a well known one, for example,from the above mentioned Japanese Laid-Open Patent Application No.3-111806, and has basically a configuration of the combination of afirst fly-eye lens-array 9 and a second fly-eye lens-array 10. In thepresent invention, particularly, the second fly-eye lens-array 10 isreplaced with two cylindrical lens-arrays 10 a and 10 b in a mutuallyorthogonal arrangement. In the present embodiment, a polarizationalignment prism array 11 of the combination of a PBS or polarizationbeam splitter array and a ½ wave plate is provided between thecylindrical lens-arrays 10 a and 10 b in order to align polarization oflight. The focusing lens 6 arranged behind the cylindrical lens array 10b serves to make a convolution of segmented luminous flux, whichsegments are formed due to division by the fly-eye lens-arrays, on theliquid crystal panel 1.

[0121] In addition to the basic configuration of such illuminationapparatus A1, a plane mirror 12 as a front mirror is attached on theinner-side surface of the front glass 8 orthogonal to the light axis ofthe collimated light as one unit in the present embodiment. That is, theplane mirror 12 is arranged orthogonal to the light axis of thecollimated light. Seen from another standpoint, a reflection surfacesymmetrical to the light axis of the collimated light through the focalpoint F of the parabolic mirror 4 is formed to be orthogonal to thelight axis and placed at the light source 3 side of the front glass 8.The plane mirror 12 is a mirror formed on a part of the inner-sidesurface of the front glass 8. A window 13 having no mirror structure,whose size is substantially the same as the size of the first fly-eyelens-array 9 as an entrance of the integrator optical system 5, isformed on the center part of the plane mirror 12. That is, the window 13is transparent for light originating from the light source 3. An AR coat14 for the window 13 is applied on the both surfaces of the front glass8 in order to improve the transparency of light.

[0122] Accordingly, in the illumination apparatus A1 in the firstembodiment according to the present invention, the collimator lens 107,the convex lens 106 and the convex lens 111 in the prior art example, tomake the size of the integrator optical system 5 compact, are allomitted and the collimated light reflected from the parabolic mirror 4or the reflector directly enters the integrator optical system 5.However, since the luminous flux generated from the light source 3cannot all be utilized by the above configuration, the luminous flux notdirectly entering the integrator optical system 5 is reflected backtoward the parabolic mirror 4 again by the plane mirror 12 beingorthogonal to the light axis of the collimated light. The reflectedluminous flux is returned to the focal point F that is the position ofthe light source 3, by the parabolic mirror 4. Herein, in the presentembodiment, since an arc lamp such as a high-pressure mercury-vaporlamp, a metal halide lamp and a xenon lamp, etc. is used as the lightsource 3, the returned luminous flux passes between electrodes of thelight source 3, reaches to the mirror surface 4 a of the parabolicsurface 4 again, is reflected by the mirror surface 4 a at once, becomescollimated light, and is directed to the integrator optical system 5from the window 13. In fact, the image formed here is an image of thelight source being several times larger than the image of the lightsource at the time of original emission so that a part of the luminousflux is blocked by the electrodes.

[0123] According to the present embodiment, while the collimated lightreflected from the parabolic mirror 4 basically exits through the window13 having no mirror surface of the plane mirror 12 toward the integratoroptical system 5, light generated from the light source 3 that does notdirectly reflect from the parabolic mirror 4 through the window 13 canbe reflected from the plane mirror 12 orthogonal to the light axis ofthe collimated light, returned to and reflected a second time on theparabolic mirror 4, and pass through the position of the focal point F,be reflected a third time on the parabolic mirror 4, and exit ascollimated light through the window 13. Hence, the parallelism of theluminous flux exiting toward the output light utilizing optical system 5is not decreased and most of the luminous flux of the light generatedfrom the light source can be utilized efficiently. Furthermore, sincethe size of the window 13 having no mirror surface and a transparencyand being substantially the same size of the first fly-eye lens-array 9placed on an entrance of the integrator optical system 5, can becontrolled, the size of the integrator optical system 5 can becontrolled to be small and usability of the luminous flux from the lightsource 3 is maintained almost independent on the shape of the integratoroptical system 5. Also, providing the plane mirror 12 attached to thefront glass 8 at the exit of the parabolic mirror 4 as one unit,precision with respect to orthogonality of the plane mirror to the lightaxis, etc., can be maintained and the configuration of the illuminationsystem is made simple.

[0124] The second embodiment according to the present invention will beillustrated with reference to FIG. 8. The same part as the partillustrated in the first embodiment is indicated with the same numeralsand the explanation about that part will be omitted. The same will beapplied for each of the following embodiments.

[0125] Although the plane mirror 12 is directly formed as one unit onthe inner surface of the front glass 8 in the first embodiment, theplane mirror 15 as a front mirror that is a member different from thefront glass 8 is provided on the inner surface or the outer surface ofthe front glass 8, perpendicularly to the light axis of the collimatedlight for the illumination apparatus A1 in the present embodiment. Theplane mirror 15 is, for example, a high-purity aluminum plate whosesurface at light source side is mirror-finished. Also, a window 16 ofwhich the shape is substantially the same as the shape of the firstfly-eye lens-array 9 is formed as an aperture in the center part of thefront glass 8.

[0126] Also in such configuration, it is clear that an effect similar tothe effect in the case of the first embodiment can be obtained.

[0127] Herein, in the illumination apparatus A2 in the presentembodiment, a convex lens 17 is provided at almost midpoint between thecylindrical lens 10 b and the liquid crystal panel 1 instead of thefocusing lens 6. The convex lens 17 also serves to make a convolution ofthe luminous flux segments formed due to division by the integratoroptical system 5 on the liquid crystal panel 1, similar to the case ofthe focusing lens 6. Particularly, since luminous flux segments formedby respective constituent lenses of the fly-eye lens-arrays 9 and 10 arecollimated between the convex lens 17 and the liquid crystal panel 1 inthe present embodiment, generation of unevenness of color can besuppressed in the case of a liquid crystal projector using a reflectionliquid crystal panel as described later.

[0128] The third embodiment according to the present invention will beillustrated with reference to FIG. 9 and FIG. 10. In the presentembodiment, only the configuration near the parabolic mirror 4 is shown.In the present embodiment, a plane mirror 15 that is a member differentfrom the front glass 8 is arranged between the front glass 8 and thelight source 3. That is, the plane mirror 15 is separated from the frontglass 8 and arranged at the light-source 3 side of the front mirror 8.The size and shape of the window 16 are the same as the size and shapeof the window shown in FIG. 8.

[0129] In such configuration, although luminous flux emitted from thelight source 3 is substantially collimated by the parabolic mirror 4,luminous flux with divergence angles of 5° through 10° are generallyincluded. Herein, according to the configuration like the presentembodiment, before the divergence of light emitted from the light source3 is increased, the light is reflected from the plane mirror 15 to holdan image of the light source formed at the focal point F due to thereflected light smaller as compared to the case of FIG. 8. Accordingly,since the divergence angle after reflection on the parabolic mirror 4and collimation can be held smaller, a drop of the efficiency at theintegrator optical system 5 is suppressed. Also in the configuration ofthe present embodiment, as indicated by the dashed lines that meanpositions capable of cutting in FIG. 10, a part of the parabolic mirror4 outside the plane mirror 15 can be cut out and the cylinder for aprojector is made thinner as described later. The same process can becarried out for the left and the right directions as well as the up andthe down directions. Also, the parts outside the plane mirror 15 for theup, the down, the left and the right directions are not cut out but theparts outside the plane mirror 15 may be in a shape of a box so that thecylinder can be similarly made thinner.

[0130] The forth embodiment according to the present invention will beillustrated with reference to FIG. 11 and FIG. 12. In the presentembodiment, a plane mirror 18 as the front mirror is provided to thefirst fly-eye lens-array 9 placed at the entrance part of the integratoroptical system 5 as one unit. More specifically, a substrate 19 madefrom the same material as the material of the first fly-eye lens-array 9is formed to have such size as an aperture of the parabolic mirror 4 canbe covered, a lens part of the first fly-eye lens-array 9 is formed intoa window 20 and a surrounding area of the window 20 is made to be amirror surface.

[0131] According to the present embodiment, the plane mirror 18 can besimply provided to decrease an adjustment part so that the cost can bedecreased. In the case of such configuration as a glass member such asUV cut glass and IR cut glass is placed between the integrator opticalsystem 5 and the parabolic mirror 4, when a part of the glass memberoutside the part through which luminous flux transmitting the firstfly-eye lens-array also passes is made to be a plane mirror, a similareffect can also be obtained.

[0132] The fifth embodiment according to the present invention will beillustrated with reference to FIG. 13 and FIG. 14. In the presentinvention, the structure of a reflector itself is devised to be acombination structure of a parabolic mirror and an ellipsoidal mirrorfor further improving usability of light.

[0133] At first, a principle with respect to the present embodiment willbe illustrated with reference to FIG. 13. Herein, the horizontal axis isthe Z-axis and the vertical axis is the-Y-axis. As the focal point of aparabola is an original point, the formula of the parabola may berepresented by y²=4f(z+f), wherein f is the focal length of theparabola. Furthermore, as a first focal point of an ellipsoid is set atthe original point, the formula of the ellipsoid may be represented byy²=−b²(z−c) ²/a²+b², wherein a is the half length of the major axis ofthe ellipsoid and b is the half length of the minor axis of theellipsoid. Also, there is a relationship of c={square root}(a²−b²)indicating a half of the distance between the first focal point and thesecond focal point. As the parabola and the ellipsoid are drawn so thatthe condition of f<a−c is satisfied, two curves have two intersectionpoints. As the intersection points are represented by l and l′, thecoordinates of the intersection points are (y₁,z₁) and (y_(1′).,z_(1′)),wherein z₁=z_(1′).

[0134] Then, as a coordinate on the Z-axis with respect to a point onthe reflection surface of the reflector is represented by z_(r), aconfiguration where both the parabola employed in the range of z_(r)<z₁and the ellipsoid employed in the range of z_(r)≧z₁ are revolved aroundthe Z-axis is employed. The ellipsoid is extended to the intersectionpoint with the minor axis and a plane mirror is placed at the positionof the minor axis. Furthermore, a window around the Z-axis is providedon the plane mirror. As a straight line “line 9” or “line 9′” throughthe second focal point and the intersection point l or l′ intersects theminor axis of the ellipsoid at the point m or m′, the size of the windowis defined as the range of m through m′. As described later, a circularwindow with a diameter of segment m m′ gives best efficiency.

[0135] Next, a principle for efficiently obtaining collimated light fromemission of the light source set at the first focal point using such aconfigured reflector will be illustrated. If a point source is placed atthe first focal point,

[0136] 1. Since a light ray emitted along line 1 is reflected from thesurface of the parabolic mirror to be parallel to the Z-axis andvertically impinges on the plane mirror as a light ray along line 2,light reflected from the surface of the plane mirror is returned alongline 2, is reflected from the surface of the parabolic mirror again,passes through the first focal point along line 1 to make a convolutionwith light directly generated from the first focal point, reaches thesurface on the parabolic mirror again, is reflected from the surface ofthe parabolic mirror, and exits out as a light ray along line 3 parallelto the Z-axis.

[0137] 2. A light ray emitted along line 4 is reflected from the surfaceof the ellipsoidal mirror and impinges on the plane mirror as light raydirecting toward the second focal point along line 5. Since the planemirror is placed at the position of the minor axis of the ellipsoid inorder to be orthogonal to the Z-axis, the light ray incident along line5 is reflected from the surface of the plane mirror along line 6directly toward the first focal point. The light ray also makes aconvolution with light directly generated from the first focal point,reaches the surface on the parabolic mirror, is reflected from thesurface of the parabolic mirror, and exits out as a light ray along line7 parallel to the Z-axis.

[0138] 3. Light ray emitted along line 6 directly impinges on the planemirror. Since the plane mirror is placed at the position of the minoraxis of the ellipsoid in order to be orthogonal to the Z-axis, the lightray is reflected from the surface of the plane mirror as a light rayalong line 5 directly away from the second focal point to the surface ofthe ellipsoidal mirror and reflected from the surface of the ellipsoidalmirror again along line 4 directly to the first focal point. The lightray also makes a convolution with light directly generated from thefirst focal point, reaches the surface on the parabolic mirror, isreflected from the surface of the parabolic mirror and exits out as alight ray along line 8 parallel to the Z-axis.

[0139]FIG. 14 shows a practical configuration example A3 of anillumination apparatus based on the principle of the diagram shown inFIG. 13.

[0140] A reflector 21 is configured by the combination of a parabolicmirror 22 and an ellipsoidal mirror 23, and line 24 indicates anintersection line of the parabolic mirror 22 and the ellipsoidal mirror23. A light source 25 is set at a focal point F of the parabolic mirror22 that is a first focal point of the ellipsoidal mirror 23. An exit ofthe reflector 21 is set at the position of the minor axis of theellipsoid and covered with a front glass 26. A plane mirror 27 as thefront mirror is provided on the inner surface of the front glass 26 asone unit. On the center part of the plane mirror 27, a rectangularwindow 28 is formed, whose size is substantially the same as the size ofthe first fly-eye lens-array 9 in the integrator optical system 5.

[0141] Herein, with respect to a relationships among the intersectionline 24 of the parabolic mirror 22 and the ellipsoidal mirror 23, theedge of the window 28 on the plane mirror 27, and the second focal pointof the ellipsoidal mirror 23, when an intersection point of line 9 orline 9′ through each end point of the intersection line 24 segment andthe second focal point of the ellipsoidal mirror 23 and the plane mirror27 is set to be outside the edge of the window 28 on the plane mirror27, usability of light becomes best for any position of the intersectionpoint on the plane mirror 27. That is, all light rays reflected from theellipsoidal mirror 23 can be returned to the light-source 3 at the firstfocal point.

[0142] Also, when light reflected from the parabolic mirror 22 isreturned by the plane mirror 27 even a little, it is effective for thedistance from the Z-axis to the top of the window 28 to exceed at least2 f. That is, luminous flux emitted along a vertical plane just at Z=0of the luminous flux emitted from the light source 3 becomes parallel tothe Z-axis by reflecting on the parabolic mirror 22, is reflected fromthe plane mirror 27 to return through the same optical path, isreflected from the parabolic mirror 22, passes through the point at Z=0,is reflected from the counter side of the parabolic mirror 22 to becomecollimated light. Since the luminous flux is reflected from the planemirror 27 to return through the same optical path, the luminous flux isdamped without exiting out of the illumination apparatus. However, evenif the luminous flux emitted along the vertical plane is sacrificed, theillumination apparatus of the present embodiment has higher efficiencythan the prior art.

[0143] Thus, according to the present embodiment, as compared to theaforementioned first through third embodiment, since light raysreflected from the surface of an ellipsoidal mirror 23 exit withreflections one time fewer than light rays reflected from the surface ofa parabolic mirror 22 to be damped a little and light rays directlyradiating from the first focal point to the plane mirror 27 can exitoutwards as collimated light to be effectively utilized, more efficientillumination is performed.

[0144] Although previous embodiments are illustrated under theassumption of a nearly ideal lamp as the light source 3, a practicallyused lamp comprises electrodes and a glass sphere sealing a gas, forwhich it is often preferred that the plane mirror 27 is slightlydisplaced on the Z-axis rather than accurately positioned at the minoraxis because of unevenness of the thickness of the glass sphere anddeviation of the position of the arc. Particularly, in a kind of DCdriven lamp, shapes of electrodes may be asymmetric and one of theelectrodes may be larger than the other electrode. Thus, when a largerelectrode is placed at the smaller coordinate on the z-axis or to theleft side in FIG. 14, in order to decrease returned light blocked by theelectrode, it is preferable that the position of an image of the secondfocal point be slightly displaced to a larger coordinate on the z-axisor to the right side in FIG. 14. It can be achieved by displacing theplane mirror 27 to larger side on z-axis than at the position of theminor axis or right side in FIG. 14. For the above operation, whenmembers of the illumination apparatus are practically assembled, outputflux of the illumination apparatus according to the present invention ismeasured and the member of the plane mirror 27 is fixed at the positionat which the value of the output flux is maximum.

[0145] The sixth embodiment according to the present invention will beillustrated with reference to FIG. 15 through FIG. 17. In anillumination apparatus A4 of the present embodiment, a polarizationconverter 31 at the entrance part of the integrator optical system 5constituting an output light utilizing optical system is employed and areflector 21 similar to the case of the aforementioned fifth embodimentis used. Herein, although the optical element 31 is called apolarization converter, the purpose and the function of the polarizationconverter are the same as those of the aforementioned polarizationalignment prism array. However, since the shape of the polarizationconverter is slightly different in terms of the relative position to theintegrator optical system 5, another name is used. The polarizationconverter 31 is provided to the first fly-eye lens-array 9 as one unit,as shown in FIG. 16. The polarization converter is configured bycombining six isosceles triangle-shaped prisms 32 a through 32 f into acentrosymmetric trapezoidal shape to form PBS or polarization beamsplitter films 33 a through 33 d on each slope of the prism. Since thePBS films 33 a through 33 d are formed to reflect S-polarization lightand transmit P-polarization light, incident collimated light from areflector 21 side is divided into S-polarization light andP-polarization light by first PBS films 33 b and 33 c located at thecenter part of the prism. The P-polarization light is transmitted by thepolarization converter and is led to the integrator optical system 5. Onthe other hand, the S-polarization light is reflected, reflected againby the outer PBS films 33 a and 33 d, which may be total reflectionmirrors alternatively, converted to P-polarization light by ½ waveplates 34 a and 34 b set on the exits of the prisms 32 a and 32 f, andled to the integrator optical system 5.

[0146] Although the function of the polarization converter 31 could beachieved by a combination of three prisms, as the polarization converteris configured by using six prisms 32 a through 32 f and symmetricallycombining two sets of three prisms in the present embodiment, compactconfiguration can be made so that the surface area on the emission-sideor integrator optical system 5 side of the polarization converter 31 istwice the surface area on the light-receiving side or reflector 21 side.That is, as the shape of the input part of the integrator optical system5 is the same as that of the case shown in FIG. 14, the surface area onthe light-receiving side of the polarization converter 31 may be half sothat the size of aperture of the window 28 on the plain mirror 27 can bealso decreased to match total size of both prisms 32 b and 32 e as shownin FIG. 15(b).

[0147] Herein, the polarization converter 31 of the present embodimentis applicable in the case of using the parabolic mirror 4 shown in FIG.7 and FIG. 8, etc. FIG. 18 shows an application example. Thus, the sizeand the shape of the window 16 on the plain mirror 15 can be decreasedto the size and the shape of the light receiving part of thepolarization converter 31.

[0148] The seventh embodiment according to the present invention will beillustrated with reference to FIG. 19. The present embodiment isimproved by taking the fabrication process of the reflector 21 intoconsideration on the condition that the reflector 21 having thestructure of a combination of a parabolic mirror and an ellipsoidalmirror is employed in order to further improve the usability of light ascompared to the aforementioned fifth embodiment.

[0149] In general, after such kind of reflector is formed by moldingmolten glass in a mold (as at least a positive die also called anarrows-die and a negative die are needed) and a mirror surface ispolished, a reflection surface is formed by means of vapor deposition.Accordingly, as an aperture is made at the minor axis of the ellipsoidalmirror surface, a tangent of the aperture is parallel to the light axisso that it is necessary to make a die in complex shape such as adividing die for removing the arrows-die. If a taper is made in-depthagainst the aperture, a glass reflector can be formed without making thearrows-die to be complex. However, as the die is simply formed in thisway, luminous flux with angle θ₂₃ and θ₂₄ shown in FIG. 19 in radiationfrom the light source 3 cannot be effectively used.

[0150] As for the solution for the problem, in the present embodiment,this reflector is made to include a second parabolic mirror so as toenable to the use of the above indicated portion of the radiationeffectively. That is, the position of the focal point of the secondparabolic mirror with a focal length f′ shorter than the focal length fof the first parabolic mirror 22 is common to the position of the focalpoint of the first parabolic mirror, the second parabolic mirror alsointersects the ellipsoidal mirror. As the intersection points aredenoted by n and n′, the coordinates of the intersection points are(y_(n),z_(n)) and (y_(n′),z_(n′)), wherein z_(n)=z_(n′). Herein, as acoordinate along the Z-axis on the reflection surface on the reflectoris denoted by z_(r), the second parabolic mirror is employed in therange of z_(r)≧z_(n).

[0151] As summarizing through the whole, in the three curves, the firstparabola is employed in the range of z_(r)<z₁, the ellipsoid is employedin the range of z₁<z_(r)<z_(n), the second parabola is employed in therange of z_(r)≧z_(n), and they are revolved around the Z-axis to formthe first parabolic mirror, the ellipsoidal mirror, and the secondparabolic mirror, respectively.

[0152] In this way, although the luminous flux with angle θ₂₄ among theluminous flux included in the angles θ₂₃ and θ₂₄ still cannot beutilized, the luminous flux included in the angle θ₂₃ can be effectivelyutilized as return light.

[0153] The eighth embodiment according to the present invention will beillustrated with reference to FIG. 20 and FIG. 21. In the aforementionedembodiments, the front mirror is configured as a plane mirror. However,in the present embodiment, the front mirror is configured as a parabolicmirror to further improve the usability of light

[0154] First, similar to the case shown in FIG. 13, the principle of thepresent embodiment will be illustrated with reference to FIG. 20.Similar to the case described above, the horizontal axis is the Z-axis,the vertical axis is the Y-axis, and as a focal point of a parabolaforming the first parabolic mirror is an original point, the formula ofthe parabola 1 may be represented by y²=4f(z+f) similar to the caseshown in FIG. 13, wherein f is a focal length of the parabola 1. Also,as a focal point of a parabola 2 forming the second parabolic mirrorfacing to the opposite direction of the first parabolic mirror is set atan original point, the formula of the parabola 2 is represented byy²=−4g(z−g), wherein g is the focal length of the parabola 2. Inaddition, the distance from the Z-axis to the top of a window of thefront mirror is represented by w and the intersection points of thesecond parabolic mirror are represented by m and m′ which arerepresented on the curve M among curves M, M′ and M″ represented asparabola 2 in FIG. 20.

[0155] The principle of the method for using emissions from the lightsource 3 effectively as collimated light using the reflector configuredin this way will be illustrated. Herein, in general, in order to insert,mount and hold the light source 3 to the reflector, it is necessary toprovide a substantially cylindrical hole (φd) revolved about the Z-axiswith y=d/2. That is, in the first parabolic mirror, this half portioncannot be a mirror surface, and consequently not all areas of thesurface can be utilized. Also, the principle is explained under thecondition that luminous flux cannot be physically emitted in thedirection of the position of the electrodes with respect to the propertyof the light source. A segment from the original point to theintersection point m is at the maximum inclusive angle or a coverageangle θ of luminous flux emitted from the light source on the lightaxis.

[0156] As a point source is placed at the original point or the focalpoint:

[0157] 1. A light ray along line 1′ not shown in FIG. 20 just slightlyinside an intersection point of a line 10 and the parabolic mirror 1becomes parallel to the Z-axis and is emitted outward (right directionin FIG. 20).

[0158] 2. A light ray along line 1 just slightly outside an intersectionpoint of the line 10 and the parabolic mirror 1 becomes parallel to theZ-axis and is directed toward the right direction along the line 10,however, the light ray is reflected from the surface of the parabolicmirror 2 and returns to the original point along the line 5, and furtheris directed to the parabolic mirror 1.

[0159] The light ray on the line 5 makes a convolution with a light raydirectly generated from the light source, is reflected at theintersection point of the parabolic mirror 1, becomes parallel to theZ-axis, and is emitted outward (right direction in the FIG. 20) from thewindow along the line 9.

[0160] 3. An emitted light ray on the line 5 from the first time isreflected from the parabolic mirror 1, becomes parallel to Z-axis, isdirected to the parabolic mirror 1 along the line 10, becomes a lightray along-the line 1 at the intersection point, returns to the originalpoint and further is directed to the parabolic mirror 1.

[0161] The light ray on the line 1 makes a convolution with a light raydirectly generated from the light source, is reflected at theintersection point of the parabolic mirror 1, becomes parallel toZ-axis, and is emitted outward (right direction in FIG. 20) from thewindow along the line 6.

[0162] 4. An emitted light ray on the line 2 from the first time makes aconvolution with the directly emitted light ray based on the principlesimilar to the case 2 and is emitted outward along the line 8.

[0163] 5. An emitted light ray on the line 4 from the first time makes aconvolution with the directly emitted light ray based on the principlesimilar to the case 3 and is emitted outward along the line 7.

[0164] 6. A light ray directly emitted to the intersection point of theparabolic mirror 1 and the parabolic mirror 2, which is not shown inFIG. 20, returns to the original point again in-principle, makes aconvolution with the directly generated light ray, is reflected from theparabolic mirror 1 again to become parallel to Z-axis and is emittedoutward.

[0165] In this way, among luminous flux generated from the light source,luminous flux with a radiation angle in the range of |θ|-|θ′| is emittedoutward as effective collimated light so that luminous flux from thelight source 3 can be utilized effectively.

[0166] Furthermore, as compared to the method in which a plane mirror isemployed as the front mirror, since the light source 3 has a volume (nota point source), the light source 3 is not completely collimated lightso that the light is reflected with confused angles on the plane mirror.However, according to the present embodiment, since the confused anglesare made small by the parabolic mirror 2 and the light is reflected,load of a subsequently used optical element is decreased.

[0167] Next, the relationship between the parabola 2 and m or m′ will beillustrated by curves M, M′ and M″. Among these, the curve M is at anideal position. That is, the absolute value of the Y-coordinate of theintersection point of the line 5 and the parabola 1 is y=d/2, the focallength g of the parabola 2:

y ²=−4g(z−g)

[0168] is decided so that the parabola 2 is at the position where theintersection point with the line 5 and the line 10 is at m.

[0169] In this way, the luminous flux with radiation angles in the rangeof |θ|-|θ′| as described above can all be used effectively.

[0170] As the parabola 2 is placed at the curve M′ outside the curve M,a light ray reflected at the intersection point of the line 10 and theparabola 2 is directed to the original point outside of the line 5, andthe light ray intersects the parabola 1 on a extension line of thedirection. The absolute value of the y-coordinate of the intersectionpoint is smaller than y=d/2 and the light ray enters the hole forholding the lamp so that the light ray cannot be taken as effectivelight.

[0171] As the parabola 2 is place at the curve M″ inside the curve M,the intersection point of the line 10 and the parabola 2 is inside theline 5 so that a light ray along the line 5 generated from the lightsource does not become collimated light and is emitted outward. That is,the coverage angle θ becomes small and the amount of useless flux inluminous flux emitted from the light source 3 is increased.

[0172] Thus, it is clear that as compared to the position of the curveM, although efficiency at the positions of curves M′ and M″ is somewhatreduced, it is much more effective than methods in the prior art.

[0173] Also, the position of explosion proof glass is decidedindependently on the curves in FIG. 20 in order to place the explosionproof glass at the position where a supporter for the electrodes istaken inside because of the shape of the light source. If by drilling ahole to pierce the supporter for the lamp electrodes of the lightsource, rendering the supporter for the lamp electrode shorter, andchanging the relation between the focal length of the parabola 1 and thefocal length of the parabola 2, the supporter for the lamp electrodescan be taken inside, the explosion proof glass may be located at any ofthe positions of curves M, M′ and M″. That is, explosion proof glass inthe shape of the parabola 2 is formed and a mirror with window is formedon one surface of the explosion proof glass to make it possible todecrease the number of members.

[0174] Next, the shape of a window 26 provided on a second parabolicmirror 35 will be illustrated with reference to FIG. 21. Herein, it isassumed that the size of a lens element constituting the aforementionedfly-eye lens-array 9 of the integrator optical system 5 is H=4 mm in thehorizontal direction and V=3 mm in the vertical direction and thefly-eye lens-array is configured so that 7×9 lens elements are arranged.

[0175] On such conditions, the basic shape of the window is arectangular shape of the horizontal side of 4 mm×7=28 mm and thevertical side of 3 mm×9=27 mm.

[0176] However, for a later-mentioned projector using a reflection LCD,the smaller the incidence angle of light entering the LCD panel surfaceis, the more the performance for contrast and color unevenness isimproved. Hence, the luminous flux passing through a diagonal lenselement, of which the incidence angle is relatively large, may not beused. In addition, in the present embodiment, the luminous flux reachingto the diagonal lens element can be reflected, utilized again, and madehigh-quality luminous flux near the center so that overall efficiencycan be improved.

[0177]FIG. 21(a) shows an example in which a range covering one diagonallens element is a reflection surface or a part of the second parabolicmirror 35 and FIG. 21(b) shows an example in which a range covering eachof three diagonal lens elements is a reflection surface or a part of thesecond parabolic mirror 35. Herein, numerical values in parenthesis inFIG. 21 are (x, y, l), that is, show x-coordinate, y-coordinate of thecorresponding point, and a diagonal length 1 being point symmetric aboutthe original point, respectively. In the case of FIG. 21(b), the minimumdistance of the window 36 is 24.2 mm so that it is advantageous that theposition of the line 10 is rendered w=12.1 mm in FIG. 20. This issimilar to the case of the aforementioned embodiments using a planemirror as the front mirror.

[0178] Furthermore, if the light axis can be set precisely andmaintained, it is not necessary to configure the window in the lenselement unit shown in FIG. 21(c) or FIG. 21(d). FIG. 21(c) is an exampleof forming the window 36 in the shape of an ellipsoid or a circleinscribing the rectangle profile and FIG. 21(d) is an example ofdividing the four sets of the three lens elements on the four corners bythe diagonal lines and forming the entire window 36 in the shape of anoctagon. In the examples of FIG. 21(c) and FIG. 21(d), since luminousflux passes through only a part of a lens element, unevenness ofilluminance may be caused in only one lens elements however, theilluminance caused by the convolution with respect to all the lenselements causes little unevenness of illuminance by mutual compensation.Particularly, in the example shown in FIG. 21(d), two lens elementslocated on each of the four corners is in a relationship to compensateits diagonal lens element completely so that unevenness of illuminanceis not caused at all theoretically. The minimum distances of bothwindows 36 are the same as the case of the rectangle 27 mm and thereforew=13.5 mm.

[0179] Thus, according to the present embodiment, by shaping luminousflux entering an integrator optical system into a circle or near circle,an luminous flux reaching to its periphery is reflected, utilized again,and made into high-quality luminous flux near the center so that overallefficiency can be improved.

[0180] Herein, for example, the position of the mirror surface of thesecond parabolic mirror 35 in FIG. 20 may be M′, the explosion proof(the front glass 8) and the second parabolic mirror 35 may be in oneunit, and further may also be configured in one unit with the firstfly-eye lens-array 9 of the integrator optical system 5, shown in FIG.22 and FIG. 23 in principle.

[0181] The ninth embodiment according to the present invention will beillustrated with reference to FIG. 24 and FIG. 25. The presentembodiment shows a configuration example of a specific illuminationapparatus A5 using the second parabolic mirror as the front mirror inthe aforementioned principle of the embodiment.

[0182] The parabolic mirror 4 (f=6 mm) for the reflector is made fromreinforced glass and the second parabolic mirror 35 (g=21 mm) as thefront glass is made from reinforced glass or normal glass. The insidesof both mirrors are formed as mirror surfaces. In this case, bothexpanding coefficients are almost same so that both mirrors are fixed bymeans of a thermostable adhesive. A part between the parabolic mirror 4and the explosion-proof glass (the front glass 8) is formed into acylindrical form with an elimination gradient by a fabrication mold.There is a substantially cylindrical drilled hole 37 for inserting,mounting and holding the light source 3 to the reflector or theparabolic mirror 4 and a hole for leader lines 38.

[0183] The tenth embodiment according to the present invention will beillustrated with reference to FIG. 26 and FIG. 27. Although anillumination apparatus A6 of the present invention is basically similarto the case of the illumination apparatus A5, an application example isshown in the case of the second parabolic mirror 35 as the front mirrormade from a metal such as high brightness aluminum and stainless steel,etc.

[0184] In this case, since reinforced glass is used in the parabolicmirror 4, the thermal expansion coefficients are different from eachother and as both mirrors are fixed, the second parabolic mirror 35 maybe deformed by heat generated at time of lighting the lamp. Accordingly,in the present embodiment, the parabolic mirror 4 and the secondparabolic mirror 35 are not fixed by an adhesive, etc. but rendered freerelative to each other and they are held at their arranged positions byspring members 39 applying a force holding the parabolic mirror 35 at asymmetrical position around Z-axis relative to the parabolic mirror 4.More specifically, four plate spring pieces 39 b are formed in crossmultiplication in mutual opposite sides by notches around a rectangularaperture formed so as not to obscure the window 36 at the center of theplate member 39 a with elasticity such as provided by stainless stealand phosphor bronze. The plate member 39 a is arranged directly belowthe explosion proof glass or the front glass 8 and fixed with the mainbody of the parabolic mirror 4 by an adhesive. The spring member 39 isnot limited to the arrangement shown in FIG. 26 and FIG. 27 and may be aline-shaped spring and a coil spring, etc. In brief, if the springmember is arranged so that a force directed toward the parabolic mirror4 is applied to the second parabolic mirror 35 symmetrically around theZ-axis, its shape is immaterial.

[0185] The eleventh embodiment according to the present invention willbe illustrated with reference to FIG. 28. The present embodiment shows,for example, an application example in which the aforementionedillumination apparatus A5 or A6 is employed for illumination of a liquidcrystal panel 1, similar to the case of FIG. 7, FIG. 8, FIG. 17 and FIG.18, etc. The illumination apparatus A5 is shown in FIG. 28. In thiscase, as for an integrator optical system 5, one similar to theaforementioned case can be used. However, herein, an example is shown inwhich instead of the first fly-eye lens-array 5, as a correspondingmember, orthogonal cylindrical lens arrays 71 a and 71 b are used andthe window 36 on the second parabolic mirror 35 is formed tosubstantially correspond to the sizes of the orthogonal cylindrical lensarrays 71 a and 71 b. Also, a shielding plate array 72 is arranged infront of the polarization alignment prism 11 that is arranged betweenthe orthogonal cylindrical lenses 10 a and 10 b corresponding to thesecond fly-eye lens-array. Also, a UV/IR cutting filter is indicatedwith the numeral 73. Furthermore, similar-to the case of FIG. 8, aconvex lens 17 is placed almost at the midpoint between the cylindricallens 10 b and the illuminated surface, wherein the focal length ismatched to the distance from the convex lens 17 to the liquid crystalpanel 1. Luminous flux divided into the segments by means of the secondfly-eye lens-array or the orthogonal cylindrical lenses 10 a and 10 boverlap on the liquid crystal panel 1 being the illuminated surface.

[0186] By taking such configuration, from the convex lens 17 to theliquid crystal panel 1 being the illuminated surface, the luminous fluxsegments made by each component lens of the fly-eye lens-array arecollimated light so that and it is advantageous that unevenness of coloris hardly caused, particularly in the case of a projector using thereflection liquid crystal panel 1.

[0187] The twelfth embodiment according to the present invention will beillustrated with reference to FIG. 29. The present embodiment shows, forexample, an example of an application of the illumination apparatus A1shown in FIG. 7 to a liquid crystal projector. Herein, in theillumination apparatus A1, a UV/IR cutting glass 41 is placed in frontof the first fly-eye lens-array 9 and a mirror 42 is inserted forchanging illumination direction by 90° between the first and the secondfly-eye lens-arrays 9 and 10.

[0188] Collimated light aligned in S-polarization by the illuminationapparatus A1 is divided into each color component R, G and B by dichroicmirrors 43 and 44 or prismatic mirrors and a total reflection mirror 45.Each component is led to a corresponding PBS or polarization beamsplitter 46, 47, or 38, is reflected from the PBS film, and illuminatesa reflection liquid crystal panel 1B, 1G or 1R respectively. 2B, 2G and2R indicate condenser lenses and 49 and 50 indicate relay lenses.

[0189] Since each reflection liquid crystal panel 1B, 1G or 1R reflectsand returns a pixel image about which an image signal provided from animage information control unit (not shown) is in OFF state, the pixelimage is reflected from the PBS film again and returned to theillumination apparatus A1-side. On the other hand, since an image in ONstate is converted to P-polarization and reflected, the image istransmitted through a PBS film and reaches to the light mixing prism 51using a dichroic prism. Each color image is mixed on a dichroic film ofthe light mixing prism 51 and passes through a projection lens 52 as aprojection lens system to project and image a liquid crystal paneldisplay image on a screen 53.

[0190] The thirteenth embodiment according to the present invention willbe illustrated with reference to FIG. 30. The present embodiment shows,for example, an example of an application of the illumination apparatusincluding the integrator optical system 5 using the convex lens as shownin FIG. 8 emitting to a liquid crystal projector. Herein, a UV/IRcutting glass 41 is provided in front of the first fly-eye lens-arrayand a plane mirror 60 is attached on one side of the UV/IR cutting glass41.

[0191] Collimated light aligned to P-polarization by the illuminationapparatus is led to a PBS 61, transmitted through the PBS, and furtherled to a light dividing and light mixing prism 62 using a dichroicprism. Here, the collimated light is divided into color components R, Gand B, which illuminate corresponding reflection liquid crystal panels1R, 1G and 1B, respectively. Since each reflection liquid crystal panel1B, 1G or 1R reflects and returns a pixel image about which an imagesignal provided from an image information control unit (not shown) is inOFF state, after mixing on the light dividing and light mixing prism 62,the pixel image is transmitted through the PBS film of the PBS 61 againand returned to the illumination system. On the other hand, since animage in ON state is converted to S-polarization and reflected, aftermixing on the light dividing and light mixing prism 62, the image isreflected from a PBS film of the PBS 61 and display images on reflectionliquid crystal panels 1R, 1G and 1B are projected and imaged on a screen64 through a projection lens 63 as a projection lens system.

[0192] Also, in the example shown in FIG. 30, taking glass density intoconsideration, the relationship of the optical distances in theintegrator optical system 5 is set to satisfy l₁+l₁′≅l₂.

[0193] Furthermore, the illumination apparatus, which is a combinationof the reflector and the integrator optical system with respect to theliquid crystal projector shown in the twelfth or the thirteenthembodiment, is only selected to illustrate an effect of the presentinvention simply, and none of the combinations of the illuminationapparatuses in the aforementioned embodiments deviates from the spiritof the invention. Particularly, with respect to the shape of thereflector, it is no problem to use any of the aforementioned shapes forany purpose.

[0194] Also, the twelfth and the thirteenth embodiments illustrateexamples of application of the projector using the reflection liquidcrystal display largely dependent on the angle of the illuminatingradiation. However, since the essence of the present invention isimproved light gathering power, it goes without saying that the presentinvention is applicable to a projector using transmission liquid crystalprojector and a projector using a DMD or dynamic mirror device. In thiscase, the polarization conversion function can be omitted.

[0195] The fourteenth embodiment according to the present invention willbe illustrated with reference to FIG. 31 and FIG. 32. First, withreference to FIG. 31, a principle of the illumination apparatus of thepresent embodiment according to the present invention will beillustrated. The illumination apparatus of the present embodiment ischaracterized in that an ellipsoidal mirror with a first focal point F1and a second focal point F2 is employed as a reflector 1. Herein, a linethrough the first focal point F1 and the second focal point F2 isreferred to as the light axis and is represented by the Z-axis. Also, anaxis on the paper surface orthogonal to the Z-axis at the first focalpoint is referred to as the Y-axis and an axis orthogonal to the papersurface is referred to as the X-axis. Hence, the first focal point is anoriginal point. In addition, a segment being a half of a major axis ofan ellipsoid is denoted by a, a segment being a half of a minor axis isdenoted by b, and a segment being a half of the distance between thefirst focal point F1 and the second focal point F2 is denoted by “c”, anellipsoidal mirror constituting a reflector 1 is formed by a part of acurve (a half along the direction of the major axis) formed by revolvingan ellipsoid represented by:

y ²=−(b ² /a ²)(z−c)² +b ²

[0196] around the Z-axis. On a part of such reflector 1, a light sourceholding hole 3, with a diameter of d, for supporting the light source 2of an arc lamp is formed and the reflector 1 includes a part not servingas an ellipsoidal mirror for the light source holding hole 3.

[0197] For such reflector 1, a plane mirror 4 as the front mirror isarranged orthogonal to the Z-axis and on the minor axis or on the x′-y′plane of the ellipsoidal mirror. The plane mirror 4 has a mirror surfaceat the first focal point side and a window 5 is formed as an aperturewith a width or diameter of w near the center, that is near the Z-axis,of the mirror surface for controlling an incidence angle to a collimatorlens. That is, the window 5 has no mirror surface.

[0198] Furthermore, a light source 2 is arranged near the first focalpoint F1 of the ellipsoidal mirror of the reflector 1. The light source2 has the length along the Z-axis of T.

[0199] A principle of the method for directing luminous flux generatedfrom the light source 2 arranged near the first focal point to thesecond focal point F2 efficiently using the reflector 1 with the planemirror 4 configured in this way will be illustrated. First, an openangle α of the luminous flux is determined by the size of the lightsource 2 (the length along Z-axis: T), an incidence angle θ′ into thereflector 1, and a distance t from the light source 2 to the reflector1. That is, the open angle is represented by α=tan⁻¹{(T/t)sin θ′}. Theopen angle becomes the maximum about the luminous flux reflected nearthe point py on the Y-axis in the ellipsoidal mirror. As luminous fluxreflected at the point p0 (to the left of the point py) on theellipsoidal mirror is noted, the above open angle is an open angle α ofthe luminous flux directly reflected from the reflector 1.

[0200] As luminous flux is reflected at the point p1 (to the right ofthe point py) on the ellipsoidal mirror, the luminous flux is directedtoward the second focal point F2, but the luminous flux is reflectedfrom the plane mirror 4 and is directed to the first focal point F1again, as if the light source 2 were placed at the second focal point F2and the luminous flux were reflected at the point p1′ and directed tothe first focal point F1. The luminous flux passes through near thefirst focal point F1 and is reflected from the reflector 1 again. Sincethe mirror surface at that point is a concave surface of the ellipsoidalmirror, the divergent luminous flux is reflected to be focused orclosed. Of course, since the centerline of the luminous flux is throughthe second focal point F2, the open angle of the focused luminous fluxis the same angle as the open angle of the luminous flux directlyreflected from the reflector 1. Herein, the open angle of the focusedluminous flux is referred to β. That is, the luminous flux reflected atthe point p1 is directed to the second focal point with an open angleα′. Afterward, the luminous flux is reflected from the plane mirror 4and subsequently the reflector 1 respectively, and finally the luminousflux is directed to the second focal point F2 with an open angle β′.

[0201] Herein, the size W of the window formed on the mirror plane 4 sothat a coverage angle θ is large is decreased, the luminous flux passesthrough the route: the reflector 1→the plane mirror 4→the reflector 1,enters the light source holding hole 3 with the diameter d for the lightsource 2. Luminous flux larger than the above luminous flux passesthrough the route: the plane mirror 4→the reflector 1→the reflector 1,for which luminous flux it is necessary to avoid entering the lightsource holding hole 3. That is, it is necessary for the size w of thewindow to be set to the size larger than the conic surface defined bythe intersection point of the line through the point pd on the edge ofthe light source holding hole 3 and the first focal point F1 and theminor axis.

[0202] Furthermore, as luminous flux directed to the point p′2 is noted,the luminous flux is reflected from the plane mirror 4, subsequentlyreflected at the point p2 on the reflector 1 and directed to the firstfocal point F1, as if the light source 2 were placed at the second focalpoint F2 and the luminous flux is directed to the first focal point F1.In this case, an arc image formed on the first focal point is smallerthan the arc of the light source 2. After the luminous flux passesthrough near the first focal point F1, the luminous flux is reflectedfrom the reflector 1 again. Since the mirror surface at that point isalso a concave surface, the divergent luminous flux is reflected to befocused or closed. Of course, since the centerline of the luminous fluxis through the second focal point F2, the open angle of the focusedluminous flux is the same angle as the open angle of the luminous fluxdirectly reflected from the reflector 1. Herein, the open angle of thefocused luminous flux is referred to γ. That is, the luminous fluxreflected at the point p2 of the reflector 1, after being reflected fromthe plane mirror 4, is directed to the first focal point F1 with an openangle α″. Afterward, the luminous flux is reflected from the reflector 1again, and directed to the second focal point F2 with an open angle γ″.

[0203]FIG. 32 shows a configuration example of the more practicalillumination apparatus A1 configured so that a collimator lens 6constituting at least one part of a collimation means is included underthe above mentioned principle. The collimator lens 6 is arranged behindthe second focal point F2 on the Z-axis. Herein, the collimator lens 6is configured with a convex lens whose focal point is at the position ofthe second focal point F2. It is common that the collimator lens 6 isconfigured with a plurality of lenses including a concave lens forreducing chromatic aberration, but the collimator lens may be one aspherical lens. A specific set position of the collimator lens 6 dependson the size of the integrator optical system arranged behind thecollimator lens 6, etc. and the collimator lens 6 is set at the bestposition indicated by L and L′, etc.

[0204] In FIG. 32, lines l and l′ through one of the intersection pointsof the ellipsoidal mirror constituting the reflector 1 and the Y-axisand the second focal point F2 of the ellipsoidal mirror are shown. Theintersection points of the lines l and l′ and the Y′-axis are alsoindicated by m and m′ respectively. About light rays shown in FIG. 32,after a light ray along the line 1 is reflected from the ellipsoidalmirror along the line 2, the light ray is reflected from the planemirror 4 along the line 3, passes through the first focal point F1, isreflected from the ellipsoidal mirror along the line 4 and is directedto the second focal point F2 to enter the collimator lens 6. A light raybeing directed to the opposite direction along the line 1 is reflectedfrom the ellipsoidal mirror and along the line 5 directed to the secondfocal point to enter the collimator lens 6. A light ray along the line 6is first reflected from the plane mirror 4 along the line 7,subsequently, is reflected from the ellipsoidal mirror along the line 8,passes through the first focal point F1, is reflected from theellipsoidal mirror along the line 9 and directed to the second focalpoint F2 to enter the collimator lens 6. Conversely, after a light rayalong the line 8 is reflected from the ellipsoidal mirror along the line7, the light ray is reflected from the plane mirror 4 along the line 6,passes through the first focal point F1, is reflected from theellipsoidal mirror along the line 10 and is directed to the second focalpoint F2 to enter the collimator lens 6.

[0205] Of course, for light rays emitted from the light source 2, lightrays directed to the opposite direction of the illustrated ones alongthe lines 6 and 8 are reflected from the ellipsoidal mirror and thelight rays are directly directed to the second focal point F2 along thelines 10 and 9 respectively.

[0206] Herein, it should be noted that as the size of the window 5 onthe plane mirror 4 is decreased to less than the size defined by thepoints m and m′ at which lines l and l′ intersect, among the light raysemitted from the first focal point F1, a light ray directed from thelight source 2 to the region inside the points m and m′ on the planemirror 4 passes through the route: the plane mirror 4→the reflector1→the reflector 1→the plane mirror 4→the reflector 1, afterward reachingto the second focal point F2 and the number of reflections is increasedtwo times more, so that an amount of attenuation is increased so as tobe not effective.

[0207] According to the present embodiment, to the reflector 1 made bythe ellipsoidal mirror, the plane mirror 4 on which the size w of thewindow 5 is defined to a certain size is arranged at the position of theminor axis, the coverage angle θ of the reflector 1 can be substantiallytaken to be large so that the luminous flux generated from the lightsource 2 can be focused to the second focal point F2 and the incidenceangle ψ can be made small, so that the luminous flux enters thecollimator lens 6. Thus, collimated light can be obtained efficiently.

[0208] The fifteenth embodiment according to the present invention willbe illustrated with reference to FIG. 33. The same part as the partillustrated in the fourteenth embodiment is indicated by the samenumerals and the illustration about the part will be omitted. The samewill be applied for each of the following embodiments.

[0209]FIG. 33 shows a configuration example of the more practicalillumination apparatus A2 configured so that a collimator lens 7constituting at least one part of a collimated means is included. Thecollimator lens 7 is arranged between the plane mirror 4 and the secondfocal point F2 on the Z-axis. Herein, the collimator lens 7 isconfigured with a concave lens system whose focal point is at theposition of the second focal point F2. It is common that the collimatorlens 7 is configured with a plurality of lenses including a convex lensfor reducing chromatic aberration, but the collimator lens may be oneaspherical lens. A specific set position of the collimator lens 7depends on the size of the integrator optical system arranged behind thecollimator lens 7, etc. and the collimator lens is set at the bestposition indicated by L and L′, etc.

[0210] In the case of the present embodiment, the same effect as thecase of the fourteenth embodiment can be obtained.

[0211] The sixteenth embodiment according to the present invention willbe illustrated with reference to FIG. 34 and FIG. 35. First, withreference to FIG. 34, a principle of the illumination apparatus of thepresent embodiment according to the present invention will beillustrated. The illumination apparatus of the present embodiment isalso characterized in that an ellipsoidal mirror with a first focalpoint F1 and a second focal point F2 is employed as a reflector 1. Atthe first focal point the light source 2 of an arc lamp is arranged. Inthe present embodiment, instead of the plane mirror 4, a sphericalmirror 11 is arranged as the front mirror. The spherical mirror 11 isformed so that the position of the center is at the second focal pint F2and a convex mirror surface with radius r is at the first focal point F1side, and the spherical mirror is arranged between the first focal pointF1 and the second focal point F2. On such spherical mirror 11, a window12 is formed as an aperture with the size to control an incidence angleto a collimator lens, near the center of the mirror surface, that is,near the Z-axis.

[0212] A principle of the method for directing luminous flux generatedfrom the light source 2 arranged near the first focal point to thesecond focal point F2 efficiently using the reflector 1 with thespherical mirror 11 configured in this way will be illustrated. First,as described in the fourteenth embodiment, an open angle α of theluminous flux is decided by the size of the light source 2 (the lengthalong the Z-axis: T), an incidence angle θ′ into the reflector 1, and adistance t from the light source 2 to the reflector 1. That is, the openangle is represented by α=tan⁻¹{(T/t) sin θ′}. The open angle becomesthe maximum about the luminous flux reflected near the point py on theY-axis in the ellipsoidal mirror.

[0213] As luminous flux reflected at the point p0 (to the left of thepoint py) on the ellipsoidal mirror is noted, the above open angle is anopen angle α of the luminous flux directly reflected from the reflector1.

[0214] As luminous flux is reflected at the point p1 (to the right ofthe point py) on the ellipsoidal mirror, the luminous flux with an openangle α is directed to the second focal point F2, but the luminous fluxis reflected from the spherical mirror 11. In this case, a furtherdivergent luminous flux is reflected. In the luminous flux, a centerlight ray emitted from the first focal point is just the same as thelight ray generated from the point source placed at the second focalpoint F2, reflected at the point P1 and directed to the first focalpoint. However, in the entire luminous flux, since the luminous flux isdivergently reflected from the spherical mirror 11, when the luminousflux is reflected at the point p1 on the reflector 1, the open angle isstill more divergent than α′.

[0215] However, since the mirror surface at the point p1 is a concavesurface of the ellipsoidal mirror, the divergent luminous flux isconversely reflected to be focused or closed. The absolute value of theopen angle is smaller than that of the divergent angle before thereflection. The centerline of the luminous flux is through the firstfocal point as described above and is reflected from the reflector 1once again. Since the mirror surface at that point is a concave surface,the luminous flux is also reflected to be focused. Of course, since thecenterline of the luminous flux passes through the second focal pointF2, the open angle of the focused luminous flux is the same angle as theopen angle of the luminous flux directly reflected from the reflector 1.Herein, the open angle of the focused luminous flux is referred to δ.That is, although the luminous flux reflected at the point p1 isdirected to the second focal point with an open angle α′, the luminousflux is reflected from the spherical mirror 11 and then the reflector 1,and finally the luminous flux is directed to the second focal point F2with an open angle δ′.

[0216] In principle if the position of the spherical mirror 11 isbetween the first focal point F1 and the second focal point F2, theaforementioned matter is not changed. However, as the spherical mirror11 is arranged at the position indicated by M in FIG. 34 so that a linen from the first focal point to the intersection point of the sphericalmirror 11 and the ellipsoidal mirror or reflector 1 is a tangent of thespherical mirror 11, a luminous flux within a coverage angle θ can beeffectively utilized. As the-position of the spherical mirror 11 iscloser to the second focal point F2 than M, shielding of luminous fluxby the spherical surface occurs. Of course, the condition may be ignoreddue to another constraint. Also, an arrangement at the position such asM′ in FIG. 34 does not deviate from the idea of the present inventionalthough the coverage angle is sacrificed.

[0217]FIG. 35 shows an configuration example of the more practicalillumination apparatus A3 configured so that a collimator lens 6constituting at least one part of a collimation means is included underthe above mentioned principle. The collimator lens 6 is arranged behindthe second focal point F2 on the Z-axis. Herein, the collimator lens 6is configured with a convex lens system of which the focal point is atthe position of the second focal point F2. It is common that thecollimator lens 6 is configured with a plurality of lenses including aconcave lens for reducing chromatic aberration, but the collimator lensmay be one aspherical lens. A specific set position of the collimatorlens 6 depends on the size of the integrator optical system arrangedbehind the collimator lens 6, etc. and the collimator lens 6 is set atthe best position indicated by L and L′, etc. In FIG. 35, lines 1 and l′through one of the intersection points of the ellipsoidal mirrorconstituting the reflector 1 and the Y-axis and the second focal pointF2 of the ellipsoidal mirror are shown. The intersection points of thelines l and l′ and the Y′-axis are also indicated by m and m′respectively. About the light rays shown in FIG. 35, after a light rayalong the line 1 is reflected by the ellipsoidal mirror along the line2, the light ray is reflected from the spherical mirror 11 and returnedalong the line 2, passes through the first focal point F1, is reflectedfrom the ellipsoidal mirror along the line 3 and is directed to thesecond focal point F2 to enter the collimator lens 6. After a light rayalong-the line 4 is reflected from the ellipsoidal mirror along the line5, the light ray is reflected from the spherical mirror 11 and returnedalong the line 5, passes through the first focal point F1, is reflectedfrom the ellipsoidal mirror along the line 6 and directed to the secondfocal point F2 to enter the collimator lens 6. Furthermore, a light rayalong the line 7 is directly reflected from the ellipsoidal mirror andreturned along the line 7, passes through the first focal point F1,reflected from the ellipsoidal mirror along the line 8 and directed tothe second focal point F2 to enter the collimator lens 6. A light rayalong the line 9 is reflected from the ellipsoidal mirror along the line10 and directed to the second focal point F2 to enter the collimatorlens 6.

[0218] Herein, it should be noted that as the size of the window 12 onthe spherical mirror 11 is decreased to less than the size defined bythe points m and m′ at which lines 1 and 1′ intersect, respectively,among the light rays emitted from the first focal point F1, a light rayreflected from the reflector 1 and directed to the region inside thepoints m and m′ on the spherical mirror 11 is reflected repeatedly suchas the reflector 1→the spherical mirror 11→the reflector 1→the sphericalmirror 11 and does not have a route to reach to the second focal pointF2 so that the arrangement of the spherical mirror 11 is meaningless.

[0219] According to the present embodiment, as for the reflector 1 madeby the ellipsoidal mirror, the spherical mirror 11 on which the size ofthe window 12 is defined to be a certain size is arranged between thefirst focal point F1 and the second focal point F2 on the light axis,the coverage angle θ of the reflector 1 can be taken to be substantiallylarge so that the luminous flux generated from the light source 2 can befocused to the second focal point F2 and the incidence angle ψ can bemade small, so that the luminous flux can enter the collimator lens 6.Thus, collimated light can be obtained efficiently.

[0220] The seventeenth embodiment according to the present inventionwill be illustrated with reference to FIG. 36. As the same as thesixteenth embodiment, FIG. 36 shows a configuration example of the morepractical illumination apparatus A4 configured so that a collimator lens7 constituting at least one part of a collimation means is included. Thecollimator lens 7 is arranged between the spherical mirror 11 and thesecond focal point F2 on the Z-axis. Herein, the collimator lens 7 isconfigured with a concave lens system of which the focal point is at theposition of the second focal point F2. It is common that the collimatorlens 7 is configured with a plurality of lenses including a convex lensfor reducing chromatic aberration, but the collimator lens may be oneaspherical lens. A specific set position of the collimator lens 7depends on the size of the integrator optical system arranged behind thecollimator lens 7, etc. and the collimator lens 7 is set at the bestposition indicated by L and L′, etc.

[0221] In the case of the present embodiment, the same effect as in thecase of the sixteenth embodiment can be obtained.

[0222] The eighteenth embodiment according to the present invention willbe illustrated with reference to FIG. 37. The present embodiment showsan application example using the aforementioned illumination-apparatusA4 for illuminating, for example, a rectangular liquid crystal panel orLCD 21 with an aspect ratio of a longitudinal side and a lateral side of4:3.

[0223] That is, the illumination apparatus is configured so that thespherical mirror 11 is employed and collimation is made by thecollimator lens 7 as a collimation means in front of the second focalpoint F2 of an ellipsoidal mirror or reflector, and may be theillumination apparatus A2. In the case of the present embodiment, oneaspherical concave lens is employed as for the collimator lens 7. Afront glass attached to an aperture part at the position of the minoraxis of the reflector 1 is indicated by the numeral 22.

[0224] Also, in the case of the present embodiment, an output lightutilizing optical system arranged between the illumination apparatus A4and the liquid crystal panel 21 is an integrator optical system 23 witha polarization converter. Although the integrator optical system 23 mayhave various configurations, in the present embodiment, instead of ageneral first fly-eye lens-array, an example using an orthogonalcylindrical lens arrays 24 a and 24 b is shown. Also, a shielding platearray 27 is arranged in front of the polarization alignment prism 26that is arranged between the orthogonal cylindrical lenses 25 a and 25 bcorresponding to the second fly-eye lens-array. A UV/IR cutting filteris also indicated with the numeral 28. Furthermore, a convex lens 29 isplaced almost at the midpoint between the cylindrical lens 25 b and theilluminated surface, wherein the focal length is matched to the distancefrom the convex lens 29 to the liquid crystal panel 21. Luminous fluxdivided into segments by means of the second fly-eye lens-array or theorthogonal cylindrical lenses 25 a and 25 b overlap on the liquidcrystal panel 21 being the illuminated surface.

[0225] By taking such configuration, from the convex lens 29 to theliquid crystal panel 21 being the illuminated surface, the luminous fluxsegments made by each component lens of the fly-eye lens-array iscollimated light so that it is advantageous that unevenness of color ishardly caused, particularly in the case of a projector using thereflection liquid crystal panel 21.

[0226] In the present embodiment, with respect to a configuration of theintegrator optical system 23, even if instead of the respectiveorthogonal cylindrical lens arrays, the first and the second fly-eyelens plates are employed, the essence of the present invention is notchanged at all. In this case, it is preferred that the polarizationconverter corresponding to the polarization alignment prism 26 bearranged immediately behind the second fly-eye lens plate.

[0227] Also, as shown in FIG. 38, instead of the polarization alignmentprism 26 between the orthogonal cylindrical lenses 25 a and 25 b, thepolarization converter 31 may be arranged immediately behind theillumination apparatus A4. That is, the polarization-converter 31corresponds to an optical element at the entrance part of the outputlight utilizing optical system. Herein, as referring to a polarizationconverter, the purpose and the function of the polarization converterare the same as those of the aforementioned polarization alignment prismarray. However, since the shapes of them are slightly different fromeach other due to the relative position to the integrator optical system23, another name is used. The polarization converter 31 is provided tothe first fly-eye lens-array 35 as one unit, similar to the sixthembodiment according to the present invention as shown in FIG. 16, thepolarization converter 31 is configured by combining six isoscelestriangle-shaped prisms 32 a through 32 f into a centrosymmetrictrapezoidal shape and forming PBS or polarization beam splitter films 33a through 33 d on each slope of the prism. Since the PBS films 33 athrough 33 d are formed to reflect S-polarization light and transmitP-polarization light, incident collimated light from the illuminationapparatus A4 side is divided into S-polarization light andP-polarization light by first PBS films 33 b and 33 c located at thecenter part and the P-polarization light is transmitted by thepolarization converter to be led to the integrator optical system 23. Onthe other hand, the S-polarization light is reflected, reflected againby the outer PBS films 33 a and 33 d, which may be total reflectionmirrors alternatively, converted to P-polarization light by ½ waveplates 34 a and 34 b set on the exits of the prisms 32 a and 32 f,respectively, to be led to the integrator optical system 23.

[0228] Similar to the sixth embodiment according to the presentinvention, although the function of such polarization converter 31 couldbe achieved by the combination of three prisms, as the polarizationconverter is configured by using six prisms 32 a through 32 f andsymmetrically combining two sets of three prisms like the presentembodiment, compact configuration can be made so that the surface areaon emission side or on the integrator optical system 23 side of thepolarization converter 31 is twice the surface area on thelight-receiving side or on the reflector 1 side. That is, as the shapeof the input part of the integrator optical system 23 is the same asthat of the case shown in FIG. 37, the surface area on thelight-receiving side of the polarization converter 31, which may be halfthe size of the aperture of the window 12 on the spherical mirror 11,can also be decreased to match the total size of both prisms 32 b and 32e.

[0229] The nineteenth embodiment according to the present invention willbe illustrated with reference to FIG. 39 and FIG. 21. The presentembodiment shows an application example using the aforementionedillumination apparatus A1 for illuminating a liquid crystal panel or LCD21.

[0230] That is, the illumination apparatus is configured so that theplane mirror 4 is arranged at the minor axis of the ellipsoidal mirroror the reflector 1 and collimation is made by the collimator lens 6 as acollimation means behind the second focal point F2 of an ellipsoidalmirror, and may be the illumination apparatus A3. In the case of thepresent embodiment, the collimator lens 6 is configured so that thewhole corresponds to one convex lens by combining four convex andconcave lenses for reducing chromatic aberration. Also, in the presentembodiment, the front glass 22 attached to the aperture of theellipsoidal mirror is directly utilized as the plane mirror 4.

[0231] Also, in the case of the present embodiment, an output lightutilizing optical system arranged between the illumination apparatus A1and the liquid crystal panel 21 is an integrator optical system 41 witha polarization converter. Although the integrator optical system 41 mayhave various configurations, in the present embodiment, the same as thecase shown in FIG. 37, the integrator optical system 41 is configuredusing an orthogonal cylindrical lens arrays 24 a, 24 b, 25 a and 25 band a convex lens 42, of which the focal length matches to a distancefrom the convex lens 42 to the liquid crystal panel, is arrangedimmediately behind the last cylindrical lens array 25 b. Thus, luminousflux divided into segments by means of the orthogonal cylindrical lensarrays 25 a and 25 b overlap on the liquid crystal panel 21 being theilluminated surface. A condenser lens for passing luminous flux with theminimum diameter to a projection lens (not shown in FIG. 39) in a liquidcrystal projector is also indicated with the numeral 43.

[0232] Thus, the method of collimation after focusing once is effectivefor an illumination apparatus in a field-sequential projector. That is,flickering becomes unnoticeable by setting the color wheel at the focalpoint.

[0233] Herein, similar to the window 12 of the spherical mirror 11, theshape of a window 5 on the plane mirror 4 as the front mirror will beillustrated with reference to FIG. 21 like the eighth embodimentaccording to the present invention. For a simple illustration, theorthogonal cylindrical lens arrays 24 a and 24 b as an optical elementat the input part of the integrator optical system 41 are replaced withone fly-eye lens-array. Herein, it is assumed that the size of a lenselement constituting the aforementioned fly-eye lens-array is H=4 mm inthe horizontal direction and V=3 mm in the vertical direction and thefly-eye lens-array is configured so that 7×9 lens elements are arranged.

[0234] On such conditions, the basic shape of the window is arectangular shape of the horizontal side of 4 mm×7=28 mm and thevertical side of 3 mm×9=27 mm. if all lens elements in the shape areutilized, the window 5 on the plane mirror 4 should be made with theratio of horizontal side to vertical side of 28:27.

[0235] However, for a projector using a reflection LCD, the smaller theincidence angle of light entering the surface of the liquid crystalpanel 21 is, the more the performance for contrast and color evenness isimproved. Hence, the luminous flux passing through a diagonal lenselement, of which the incidence angle is relatively large, may not beused. In addition, in the present embodiment, the luminous flux reachingto the diagonal lens element can be reflected, utilized again, and madehigh-quality luminous flux near the center so that overall efficiencycan be improved.

[0236] Also, similar to the eighth embodiment according to the presentinvention, FIG. 21(a) shows an example in which a range covering onediagonal lens element is a reflection surface or a part of theellipsoidal mirror and FIG. 21(b) shows an example in which a rangecovering each of three diagonal lens elements is a reflection surface ora part of the ellipsoidal mirror. Herein, numerical values inparenthesis in FIG. 21 are (x, y, l), that is, show x-coordinate,y-coordinate of the corresponding point, and a diagonal length l beingsymmetric about the original point, respectively.

[0237] Furthermore, if the light axis can be set precisely andmaintained, it is not necessary to configure the window in the lenselement unit shown in FIG. 21(c) or FIG. 21(d). FIG. 21(c) is an exampleof forming the window 5 in the shape of an ellipsoid or a circleinscribing to the rectangle profile and FIG. 21(d) is an example ofdividing the four sets of the three lens elements on the four corners bythe diagonal lines and forming the entire window 36 in the shape of anoctagon. In the examples of FIG. 21(c) and FIG. 21(d), since luminousflux passes through only a part of a lens element, unevenness ofilluminance may be caused in only one lens element, however, theilluminance caused by the convolution with respect to the all lenselements causes little unevenness of illuminance due to mutualcompensation.

[0238] Particularly, in the example shown in FIG. 21(d), two lenselements located on each of the four corners are in the relationship tocompensate its diagonal lens elements completely so that unevenness ofilluminance is theoretically not caused at all.

[0239] As described above, for a simple illustration, the orthogonalcylindrical lens arrays 24 a and 24 b as an optical element at the inputpart of the integrator optical system 41 are replaced with one fly-eyelens-array. However, for the orthogonal cylindrical lens arrays, it ispossible to understand that if a similar approach would be applied to anintersection unit of a longitudinal cylindrical lens array and a lateralcylindrical lens array, a similar effect can be obtained so that adetailed description is omitted.

[0240] Thus, by shaping luminous flux entering an integrator opticalsystem into a circle or near circle, luminous flux reaching to itsperiphery is reflected, utilized again, and made high-quality luminousflux near the center so that overall efficiency can be improved.

[0241] The present invention is not limited to the specificallydisclosed embodiments, and variations and modifications may be madewithout departing from the scope of the present invention.

[0242] The present application is based on Japanese priorityapplications No. 2001-123923 filed on Apr. 23, 2001 and No. 2001-263890filed on Aug. 31, 2001, the entire contents of which are herebyincorporated by reference.

What is claimed is:
 1. An illumination apparatus in which at least onepart of a reflector is a first parabolic mirror, a light source isarranged near a focal point of the first parabolic mirror, andcollimated light that is emitted from the light source and reflectedfrom the first parabolic mirror exits toward an output light utilizingoptical system, wherein a front mirror is arranged on a light path ofthe collimated light, said front mirror comprising: a transparent windowhaving no mirror surface and a window size substantially the same as asize of an entrance part of the output light utilizing optical system;and a mirror surface at light source side that is symmetrical about alight axis of the collimated light extending through the position of thefocal point of the first parabolic mirror.
 2. The illumination apparatusas claimed in claim 1, wherein the front mirror is provided to a frontglass attached to an exit of the first parabolic mirror as one unit. 3.The illumination apparatus as claimed in claim 1, wherein the frontmirror is arranged between the front glass attached to an exit of thefirst parabolic mirror and the light source.
 4. The illuminationapparatus as claimed in claim 1, wherein the output light utilizingoptical system comprises an integrator optical system therein and thefront mirror is provided in combination with a first fly-eye lens-arrayor a member corresponding to the first fly-eye lens-array of theintegrator optical system as one unit.
 5. The illumination apparatus asclaimed in claim 1, wherein the front mirror is a plane mirror.
 6. Anillumination apparatus in which at least one part of a reflector is afirst parabolic mirror, a light source is arranged near a focal point ofthe first parabolic mirror, and collimated light emitted from the lightsource and reflected from the first parabolic mirror exits toward anoutput light utilizing optical system, the reflector comprising: thefirst parabolic mirror at least in a region where the collimated lightreflected from the first parabolic mirror covers an entrance of theoutput light utilizing optical system; an ellipsoidal mirror outside thefirst parabolic mirror having a focal point common to the focal point ofthe first parabolic mirror; and a plane mirror with a transparent windowhaving no mirror surface and a window size substantially the same as asize of an entrance part of the output light utilizing optical system,said plane mirror being arranged near a minor axis of the ellipsoidalmirror perpendicularly to a light axis of the collimated light.
 7. Theillumination apparatus as claimed in claim 6, wherein the reflectorcomprises a second parabolic mirror existing from an end of theellipsoidal mirror to the plane mirror near the minor axis and having afocal point common to the focal point of the first parabolic mirror. 8.The illumination apparatus as claimed in claim 1, wherein the frontmirror is a third parabolic mirror having a focal point common to thefocal point of the first parabolic mirror.
 9. The illumination apparatusas claimed in claim 8, wherein the position of a point at which astraight line through the focal point and a part of the third parabolicmirror at which the distance from the center of the window is minimumintersects the first parabolic mirror is outside of an intersection lineof a hole through which the light source is inserted.
 10. Theillumination apparatus as claimed in claim 1, wherein the output lightutilizing optical system has a polarization converter for aligningpolarization direction on the entrance thereof and the size of thewindow having no mirror surface of the front mirror is substantially thesame as the size of the polarization converter.
 11. The illuminationapparatus as claimed in claim 1, wherein the output light utilizingoptical system has an integrator optical system on the entrance thereofand the size of the window having no mirror surface of the front mirroris substantially the same as an effective size of the first fly-eyelens-array on the entrance of the integrator optical system.
 12. Theillumination apparatus as claimed in claim 1, wherein the output lightutilizing optical system has an integrator optical system on theentrance thereof and the size of the window having no mirror surface ofthe front mirror is substantially the same as an effective size of anorthogonal cylindrical lens-array on the entrance of the integratoroptical system.
 13. The illumination apparatus as claimed in claim 1,wherein the window of the front mirror has such size as a minimumdistance from the light axis to a part at which the collimated lightthrough the focal point of the first parabolic mirror impinges on thefront mirror is larger than two times of a focal length of the firstparabolic mirror.
 14. The illumination apparatus as claimed in claim 8,wherein the front mirror is held at a set position by a spring material.15. A liquid crystal projector comprising: at least one liquid crystalpanel on which an image projected by an image information controllingunit is formed; the illumination apparatus of claim 1 for illuminatingthe liquid crystal panel as an object illuminated by the output lightutilizing optical system; and a projection lens system for projectingthe image formed on the liquid crystal to a screen.
 16. A liquid crystalprojector comprising: at least one liquid crystal panel on which animage projected by an image information controlling unit is formed; theillumination apparatus of claim 6 for illuminating the liquid crystalpanel as an object illuminated by the output light utilizing opticalsystem; and a projection lens system for projecting the image formed onthe liquid crystal to a screen.
 17. An illumination apparatus using anellipsoidal mirror in at least one part of a reflector, arranging alight source near a first focal point of the ellipsoidal mirror andreflecting luminous flux emitted from the light source by theellipsoidal mirror to direct the luminous flux to near a second focalpoint of the ellipsoidal mirror, wherein a front mirror, on which awindow having no mirror surface is formed near a light axis extendingthrough the first focal point and the second focal point, is arrangedbetween the first focal point and the second focal point, and at leastone part of the light reflected from the ellipsoidal mirror among theluminous flux emitted from the light source is reflected from the frontmirror in front of the second focal point to be returned to theellipsoidal mirror or a vicinity of the first focal point.
 18. Theillumination apparatus as claimed in claim 17, wherein the front mirroris a plane mirror arranged orthogonal to the light axis and at theposition of the minor axis of the ellipsoidal mirror.
 19. Theillumination apparatus as claimed in claim 18, wherein the front mirrorhas the window at least in the range cut out by a conical surfaceextending from an edge of a light source holding hole formed on thereflector through the first focal point.
 20. The illumination apparatusas claimed in claim 17, wherein the front mirror is a spherical mirrorof which the center is the second focal point.
 21. The illuminationapparatus as claimed in claim 20, wherein the front mirror has thewindow at least in the range cut out by a conical surface extending fromthe intersection line of a surface orthogonal to the light axis at thefirst focal point and the ellipsoidal mirror, to the second focal point.22. The illumination apparatus as claimed in claim 17, wherein a firstoptical member of a collimation means for making collimated light isarranged behind the second focal point on the light axis.
 23. Theillumination apparatus as claimed in claim 17, wherein a first opticalmember of a collimation means for making collimated light is arrangedbetween the front mirror and the second focal point.
 24. Theillumination apparatus as claimed in claim 17, wherein the window has asimilar figure to an entrance of an optical element on the entrance partof the output light utilizing optical system.
 25. The illuminationapparatus as claimed in claim 24, wherein the optical element on theentrance part of the output light utilizing optical system is anintegrator.
 26. The illumination apparatus as claimed in claim 24,wherein the optical element on the entrance part of the output lightutilizing optical system is a polarization converter.
 27. A liquidcrystal projector comprising: at least one liquid crystal panel on whichan image projected by an image information controlling unit is formed;the illumination apparatus of claim 17 for illuminating the liquidcrystal panel as an object illuminated by the output light utilizingoptical system; and a projection lens system for projecting the imageformed on the liquid crystal to a screen.